Not to mention market share can't exceed 100%...

I think it will level out because:

(1) the quality of Firefox and IE have shot up over the last year in response to Chrome.

(2) Chrome's users are the most fickle and thus the most susceptible to new (or old) competition.

I can relate to number one, but what's your evidence for number two?

Early adopters are generally the least loyal of any customer. They are much more likely to take a risk on new technology and give it a shot.

Just an anecdote, but I have been using chrome for the last six months because everything else was slow as a dog on my Mum's MacBook Pro, and chrome was super-fast. But the lack of decent keyboard link navigation is driving me crazy, and may drive me back to firefox soon.

Interesting, I've found Chrome to be slightly faster than Safari on my MacBook, but also much more prone to stalls and complete catatonia than Safari.