I don't have a Mac (imagine how difficult it was to create a working keyboard layout without access to one), but I did E-mail the authors of fKeys and DoubleCommand. The author of DoubleCommand didn't answer my E-mail, but the author of fKeys wrote me that it is indeed possible with fKeys beta 0.2.1 and the right configuration settings. The configuration file kodachi-kinesis-bs.plist demonstrates Caps Lock to Backspace mapping (but it maps also some other things). I suggest all Mac users to write to the authors of these programs to see if they can implement this as a standard feature. You should probably also write Apple and ask them to implement this feature in the OS, so it won't require kernel extension hacks.

I remapped with fKeys.
I had to alter the configuration file though to make it compatible with my MacBook Pro.
I emailed the config file back to the author of the program, but i do not know if he has included it.

Post any difficulties you have here, and I will try to help you out.

0.2.1 is the latest version of fKeys. I've updated the link on Colemak Mac page to that version.

Oops! I had fogotten reading that in the docs that he had built it using 10.4.6 with xcode 2.2.

He goes on to suggest uControl but on installing that program I discovered that there is no way to reassign the Caps Lock key to Backspace.  You can only convert to things like the Control, Fn, and Command keys.  I am not exactly excited about trying to spend time hacking the source code of an abandoned project. 

I am going to try to get the source code for fKeys working on 10.3.9 . 
Hopefully it will be fairly trivial.

OK, I tried to make the enter key a Caps Lock key using fKeys but found the things I tried didn't work so it doesn't appear to be trivial. I probably will still find the time to ask the author about that.  But for now I am happy with an easy solution that any many ways makes more sense.  I am using the sticky keys option on the OS X universal access pane. So far I am wondering why this is not the default behavior for shift keys on computers!  The following is not for people that know but for those who stumble on this and need a quick and easy . 

Okay, my final solution on my Macbook running Tiger (OS X 10.4.8) is the following and it works great.

1.  go to https://colemak.com/Mac and download and install Colemak.layout   
     (read Shai's warnings - however in Tiger my experience is that the authetication windows and login windows always default to Qwerty layout no matter what I do. On my powerbook that is running Panther (OS X 10.3.9) that is not the case for the authentication windows - they do become Colemak layout by default however it is trivial to change back on the fly if you have turned on the "Show input menu in the menu bar" International preference pane. The login window remains Qwerty in Panther.)

2.  download fKeys beta 0.2.1 and install,  readme file

3.  download the macbook config files from the same beta page and modify them using some cut and paste magic with the Colemak example in the kinesis keyboard config files. Its pretty trivial to do as long as you are careful.   OR you can email me and I will send what I have done.  It still has the config for the powerbook keyboards and when I upgrade my powerbook to Tiger soon I will test it there to be sure.  I have in mind to put up a Colemak for the mac page to put up the files to download.

4. HAVING YOUR CAKE AND EATING IT TOO!  :-)
      get a caps lock back by turning on sticky keys in the accessibilily preference pane
      see here  http://www.apple.com/accessibility/physical/
     
      Actually, this is great and in many ways is more functional than the standard Caps Lock key. 
      I have decided this is better than dedicating another key to caps lock.  All the shift functionality in one key does make a lot
      more sense.  Why is this not standard behavior?  It would be nice I suppose if if you could just make the shift keys sticky
      only. I wonder if that can be done with fKeys?

      Note: I would turn off the beep but the display option is kind of nice for sticky keys.

all this may be obvious to some, but it wasn't to me so I hope its useful to anyone looking at Colemak on a mac. 

Craig

I am having problems mapping caps lock to backspace on my external MacBook Pro Keyboard has anyone solved this or have any clues? More details below. I tried writing the fKeys developer and have gotten no response.

I installed Craig's config for fKeys. It works with the built in keyboard, but on the external keyboard pressing the caps lock key deletes AND locks caps.

I think I need to set up a section for the external keyboard in the fKeys config file, but I can’t figure out what the key events are. I tried both

      Debug: Events EventsAll
and
      Debug: All

neither places entries in the log file similar to those described in the fKeys interpreter doc. There are other fKeys entries such as PROBE, steal, REPROBE, setProperties, etc.

Thanks,
Cathy

Great news for all us Mac users. Doublecommand now has the option to switch the caps lock key to backspace. A minor problem is that the caps not key does not continuously delete when you hold it down. That doesn't bother me that much since I'm mostly using caps lock for quick corrections.

No more ugly hacks to make the key switch - simply check a box and it works like a charm.

Get the latest version here: http://doublecommand.sourceforge.net/

Thanks to Michael who implemented this feature!!!

Sweet!!! 

  Works beautifully.   I like the options it gives you to start it automatically when you login. 

No more having to setup fKeys every time I reboot.

Yes, I use DoubleCommand for my external keyboard.  No, fKeys never worked for me.

Hey i'm using doublecommand to remap caps lock to backspace but now i have to hit capslock twice to to backspace, rather annoying. Is there a way around this?

No i'm using my macbook keyboard itself, or a microsoft erg something keyboard, it does it on both. Specifically, if you are typing a running sentence and want to backspace once, it works just fine, you hit it once and it backspaces regardless of if the capslock light is on or off. BUT, if you need to backspace more than once (say you type multiple letters incorrectly or want to backspace through a whole word), after your first backspace, it only backspaces when the backspace light is ON. So if you want to backspace and the light is currently off, you have to hit capslock to turn the light on, then hit it again to actually backspace.

I don't need a reapeating backspace, I just want to be able to backspace through the word colemak, for example, in 7 presses, not 12 as it is currently (explained in detail below).

I'm checking this as a type this post, so i'm sure. Here is what is happening in detail. If I am typing a running sentence and need to backspace once, it works regardless of whether caps lock is on the "on" (light on) or "off" (light off) positions. So if I type coleman and need to backspace the n to turn into a k, I just have to hit capslock once. But, if I want to backspace immediately again, it will only backspace if the light is on. So say I type coleman and want to delete the whole word, assuming initially the caps light is off, one hit to get rid of the n, then the light is on, second hit gets rid of the a, then the light is off, so TWO hits to get rid of the m, and the light is off, so again two hits to get rid of e, l, o, c, each. So a total of 12 hits of capslock.

I swear I've seen another post on here where someone mentioned this effect on their mac casually, but I can't seem to find it now, they said something about doublecommand working, but they had to hit caps a bunch of times to backspace through words.