I too am an Opera fan. I have paid for it and don't regret it. That said there are a lot of primary sites that don't work well with it. Microsoft (suprise) and several other support sites I visit.
I know that it's because they don't adhere to strict standards, but in the final analysis- it does make it impossible for Opera to be my ONE browser.
I would much prefer that Opera was a bit more tolerant of these sites. I've heard all the arguments about emailing the sites webmaster, boycott the site, etc. No can do. As a System Admin, I don't have the luxury of NOT going to these sites. So for most things I use Opera, but I sure wish I could use it for everything...