I commonly use Opera at home, ever since my FF install got corrupted.

I've not noticed any issues at all here. I do have occasional problems with people running non-standard CSS. Most notably, my bank's navigation bar doesn't work right, but they've got alternative links for older browsers in the footers.

Facebook sometimes doesn't like it. There are times when I can't post comments or upload images. Those problems seem to be intermittent, although there are certain apps there that never work, so I just ignore all of them now. (So for those of you trying to get me to help you in Mafia Wars, that's the reason.)