(If you can’t tell from the title, I’ve been reading too much Lifehacker lately.)
As alluded to before, I’ve been using Opera for a month or so now because Camino decided it was going to suck down all my CPU. Since only the nightly build at the time had the feature I wanted (bookmark bar, works well so far), I was forced to travel into “the land of no automatic updates.” Fortunately, I figured out how to keep all of my settings, bookmarks, and even open tabs when upgrading. Note that these steps may not be necessary, since everything might end up hunky-dory all by itself.
1. You’re probably getting your nightly builds from here. Why they use a blog (with anonymous commenting disabled, no less) for getting feedback on builds is beyond me. In any case, you should download the nightly you want to use.
2. Back up your bookmarks and your ~/Library/Preferences/Opera Preferences * folder just in case. You can also move your current Opera application bundle out of Applications and onto the desktop just in case.
3. Install the new version by opening the DMG and dragging the application bundle to your Applications directory. Don’t start the browser yet.
4. Copy the files you backed up from your Opera Preferences folder into the most recent Opera Preferences folder (there might be a version change which changes the folder name; just today I went from 10.7 to 11.0 on the folder name even though I’m using the last build of 10.
5. Start Opera (the new version). Hope things work.
Hope this helps somebody, or at the very least sets them on the right track.