At the risk of embarrassing myself after those stats, (I am hardly the poster boy for Colemak)

QWERTY
-30 years not touch typing
-5-30wpm  (upper speeds could not maintain very long, typing tests are making me appreciate just how much time I spent in the lower part of the range)
-Excellent accuracy (90%-100%)

Dvorak
-1 months
-5-20wpm  (but I hated all the movement of my right hand pivoting for L)
-Fair accuracy (it fluctuated a lot, but mostly 80%-95%)

Colemak
-4 months
-30-40wpm 
-Excellent accuracy (90%-100%)

QWERTY:
* 25+ years
* 55-60 WPM on a good day
* I think about 90% accuracy; less on a bad day

Dvorak:
* 2 years 3 months
* About 55 WPM on a good day
* 97% accuracy

Colemak:
* 5 months (started during the Xmas holiday -06)
* 49 WPM consistently (doesn't seem to improve fast now, but I'm not training either)
* 98% accuracy

(TypingMaster online test; 3 min)

This thread is very interesting.  I have only done a couple of lessons of Colemak, but here's my baseline:

Dvorak:
10 years
53 WPM
93% accuracy

QWERTY:
25 years
41 WPM
92% accuracy

(TypingMaster 3-minute test, back-to-back)

You won't be surprised that, being better at Dvorak, I'm finding Colemak a bit challenging.

New Year, time to update

Colemak
-12 months
-40-45wpm  (bursts of 55-60 wpm of up to 30 sec. but can't maintain it yet for 2 min. typing tests)
-Excellent accuracy (90%-100%)

Qwerty
15 years touch typing
Never check the speed

Colemak
1 year
Tested at Ryan Heise site: 57 wpm (I feel it is the same or slightly faster as my Qwerty speed back then).
Comment: much more comfortable typing with Colemak than QWERTY... :-)) And that makes me able to sustain longer typing session. It is a two dimension productivity increase, plus I think, it's better investment for the future of my arms and fingers... :-))

Hmmm... I've heard that anything above 95% accuracy is fair as long as your speed is good. Earlier, correcting a mistake would take long and be imperfect so naturally a much higher accuracy would be worth striving for.

Then again, there's the "beautiful typing" school that strives for as close to 100% as possible just because they feel it's the best way to learn and do. Perfection in all you do, Asian-philosophy-style. I learnt not to rehearse in mistakes when I learnt to play the piano, so I see what they mean. If you get too sloppy, you get trouble.

My own opinion is that 97% is a nice accuracy. My old QWERTY accuracy was much worse, and my Dvorak accuracy comparable to that. I have a feeling that as I keep training (Colemak now) I can do even better, but not at the moment.

[update 081125: After switching to essentially the standard Colemak ('comfort') layout, I've gone through the TypingMaster course to get used to the new stuff and learn the old stuff properly, focusing mainly on accuracy. (Unfortunately, there's no material made for Colemak in TypingMaster, but I like the program so that's what I used.) I managed to get 98% accuracy in most lessons, but only with dedication. I noted how the early lessons were very hard but after 8-10 lessons it started getting easier to keep up accuracy. I'm already reaping the benefits: My highscore on hi-games has been stable at 65 WPM for ages which was starting to annoy me, but after the course it has been improving again! First I made 66, then 67 and today 70 WPM. I take back the assumption that 95% accuracy will get you anywhere good: I think that in this day and age you should strive for better. I'm still not using the CapsLock key for Backspace; I'm hoping that I can keep pushing for accuracy and not have to use it much...]

qwerty
- a good few years
- average speed on a good day: 20wpm, once i got to 38wpm, but not for very long

colemak
- 1 week
- 11wpm

QWERTY:
- ~11 years
- 70 wpm gross (I didn't take a net speed test before switching)
- probably around 90% accuracy

Colemak:
- 1.5 years
- 60-70 wpm net
- 97-98% accuracy

Personally, I think Colemak is a better option to learn:

- Many happy users means the layout has proven effective.
- This forum for help.
- Readily available on all platforms.
- Included by default on most *nixes.
- It is stable and will not be tinkered with in the future.

Qwerty:
- 17 years
- 68 wpm average, 83 wpm maximum
- 90% accuracy average

Colemak:
- 6 months
- 73 wpm average, 95 wpm maximum
- 95-100% accuracy range, 98-99% average.

I practice each day (except sunday) since my switch to colemak (six months now).
Some key combinations are still awkward for me (..you, stereo, through ect.)
Also i have built an selfmade mechanical keyboard that i exclusively use
for colemak, my old rubber dome keyboard that i have used for qwerty
i don't longer miss ;-)