I've been 'hooked' on Opera for some time now, despite the incompatibilities that exist with it and some web sites. Opera is fast, intuitive, has great page zoom/resizing, etc.. etc..
However, I think I've finally reached my breaking point thanks to continued terrible support of Opera by virtually all of Google's 'web 2.0' services. With Opera 9.0 gmail at least works most of the time, but there is an annoying quirk on occasion that causes the editor to be mis-sized, resulting in line breaks inappropriately placed. That continued quirk, along with all the other Google service incompatibilities is enough to make me go Firefox. I'm just tired of dealing with it... and don't care who is really to blame (I'm sure Google could do much better to support Opera if they wanted).
So.. cya Opera, as much as I love thee.