Yes, if you switch you might exceed your old speed, but you might not. As DreymaR says, if speed is what you're after, a switch might not be worthwhile for you.
If you're looking for a different typing experience (generally much less flying around of fingers and hands), or have any concerns about your hands' health, you could give it a try. It's definitely a good brain exercise.

PS: With Colemak you'll need much less alternative typing techniques for certain letter combinations compared to Qwerty. But it still does take some time to adopt them.

Oh, you'll most definitely end up typing faster if you persist! Thing is though, it's hard to prove whether that's mostly because of layout benefits or because of the effort you have to put in to learn Colemak! I think if you spent all that effort on QWERTY speed training you could possibly get the same increase. It might be hard to do that right though unless you have a typing sensei. ;)

I've switched from 55 WPM QWERTY to 60 WPM Dvorak (after a lot of work) to 70 WPM Colemak (after using it since 2006). I'm a deliberate person in my forties so I may not get all that much faster but I still see a steady increase in both speed and comfort. It's not a fast progress but it's still nice. If I train for a while I see better results of course.

If you depend on your typing every day you could switch gradually with Tarmak (see my signature) and not lose much speed at any point. (Or rather, you'd lose speed but pick it up again within a day or so for each step I think.) Not many have done it but I firmly believe it's worth a try if you're interested.

Basically, it means that no matter how much I like it I will always suck at Tekken I guess... ;)

My proclivities are to deliberation rather than to twitch reactions.

For further discussion, Ryan Heise was 110wpm Qwerty typist. After a year, he is now 90wpm in Qwerty and 120-130wpm in Colemak.

He showed how to maintain fluency in both layouts simultaneously here
http://www.ryanheise.com/colemak/

His website hi-games.net has become the standard typing test that most of us use.

If you're curious the good news is I've never heard of anyone getting ruined by a layout change! If you lose a little QWERTY speed after you change to Colemak it'll a) be easy to regain should you wish to (people usually don't bother to because they love typing in Colemak) and b) usually mean that your Colemak speed now surpasses your previous QWERTY speed.

That's my firm impression at least.

That's a fair point guys, speed isn't everything.
Also it's encouraging to see that you all feel that switching to Colemak will help me to get to and maybe even surpass my previous qwerty speed, also even if that doesn't happen what with the comfort benefit and all I'm more inclined to change than ever.
But, I still have a problem in that Colemak is a niche typing layout.... what should I do if I have to type on other people's computers or my office computer which doesn't support it?. As I earn my bread and butter as a computer engineer, this is something that might be the clinching factor in making my decision. So does colemak have any portable software (preferably of low size) which I can carry around me which makes switching back and forth between the two layouts relatively easily, possible?.

@dark-side, portability was a big factor for me (I swap machines a lot) and as such selected  Dvorak as it had wide-spread support.  The good news is that it feels easier to swap and use alternative layouts than in the past.  However it's not painless.  Those times I have to fall back to Qwerty I struggle, and can look like an inept fool.

Well, it's the simple way. For a more advanced program with plenty of useful functionality, consider Portable Keyboard Layout by Farkas Máté. I'm particularly fond of the Extend mappings.

See this topic by me for a walkthrough of the cool things I've been able to do with PKL to customize my Windows typing with full portability!

Probably.

It's easy to get better home row usage! Minimak is the extreme example of that. But what you want in a decent layout is more. Same-finger digraphs are bad, for instance. Digraphs in general should be your concern, not only crude monographs.

If you are a home row (or more precisely, home position) fanatic and in addition type exclusively in English then you may notice that not everything is completely optimal for you in Colemak. The H is relatively common and could've been moved in to the home position, and the A may be considered too common for the left pinky. But considering the most frequent letters in English are (more or less) ETAOIN SHRDLU, they have all gotten decent placements in this layout. And considering all the other factors you should consider, I'd say it's hard to beat Colemak for a balanced approach. Not impossible, but hard. Many have tried and are hardly heard of anymore.

All in all, there's probably always a layout or ten that's better for you since your preferences and needs will vary from others'. But it may be hard to find and probably isn't invented yet. So you could use an algorithm to try and find it? But I don't trust those algoritms because their underlying models are oversimplified and sometimes dead wrong because the assumptions of their makers are wrong. So the only good test would be to make a layout and use it for a long time and then wash rinse repeat - and that's not easy to do! Some have done it but there's always the question of what's a long enough trial period and how biased you are based on your prior knowledge and preferences etc etc. And in the end you'll end up with a layout that's best for you, but not necessarily for many others. Fun, huh? ;)

Colemak. It's damn good. It fits lots of people's needs. It doesn't require that you carry around your own keyboard. It's got good support and several technical solutions supplied by its user mass. And it's there already.

I was merely suggesting that there must be something better and easier to use than the existing crude rectangular arrays of switches.