I'm still a firefox user, though I do like Chrome- I rotate around Opera, Firefox, and Chrome now and then. Chrome is nice and fast, but it suffers from "so what?" syndrome; there's really nothing it brings to the table that other browsers don't already bring as well (though firefox did ape Chrome's incognito window, if I recall correctly). I wouldn't discourage anyone from using it, but I don't see any obvious advantages it has over the competition.
As for changing the user-agent string, this blog here has some info on how to do it- looks like you have to hex edit the chrome.dll file. Not for the faint of heart, I suppose, but I don't think it will be too long until Chrome supports some sort of user add-on to do this automatically! (Maybe it does already, haven't used it in a couple of versions).