I went from hg -> git in the last couple of years. I'd say they are "almost identical". The key difference is a slightly different mindset on merging and branching IMHO. It can be non-trivial for some of my more hard headed dev brethren to change their way of thinking once they've chosen a method and gotten in the correct mindset.

I went from using mercurial to git and I still have lots of respect for mercurial. I wouldn't mind the switch at all if I needed to work with a team who used mercurial, but personally I still just prefer git.

Yup, that's me in a nutshell. I used svk first and then moved on to mercurial.

Then I had to learn git. I like the model for lightweight branches in git (bookmarks in mercurial) but the step backwards in UI is still irritating. I'm used to it at this point but teaching it to others is a constant source of pain ("git checkout -t/-b"!)

Ugh, no, I fought my way through git first, and I didn't think hg was the same when I encountered it, I thought hg was nigh-unusable after I thrashed at it for a week.