Glad you brought this thread up blurrymind!
I've always been a "Mozilla App" person myself and have kept "the other guy" (Opera 9.5*) around for whenever I wanted a break in the routine. One day when taking such a break it opened up to the "Would you like to test drive Opera 10?" page and I thought, "Sure! Why not? I can't dance!"
I've loved it so much
that I've become about 50/50 now in my browsing habits between SeaMonkey and Opera. For email, however, I've still remained with SM/TBird as the Opera 10 client is yet quite buggy in that regard. But hey---it's an alpha build. When they finish with it who knows? I'm impressed with what I've seen of the email client that's for sure---it just can't handle my volume of email.
As for the browser though: I haven't had a single crash to date. Even they say that the bittorrent client doesn't work and yet it's worked for me. Go figure! The one problem which I have experienced, however, is that sometimes if a link is... how do they say it now?... "java-related" I think it's called? Then those links won't function whereas plain html-formatted links do work. I can't recall precisely where I'd run into this problem, whether it was trying to follow up on another distro review at Linux.com or one of Vaughan-Nichol's reviews, but the links at the bottom wouldn't "click". Returning in SeaMonkey the links worked just fine.
And that's been my one and only problem to date. Of course I don't do a lot of "heavy surfing" like some do. I have just specific pages and forums I visit and that's basically it. But I've enjoyed it so much so that I've replaced my 9.5* and 9.6* versions everywhere in my 6 distros (except Wolvix as the libc is outdated) to the new Opera 10.