I have Windows XP, SP3 on an Intel Pentioum 4 2.80 ghz cpu, 2gb memory, ati all in wonder 9600XT...and have been using opera on and off for a few years, but had to back off because it could not open my aol email...however, i started using opera 10 since alpha, thats Dec 2008 or so...and have been impressed with it so far, for the most part....now the opera 10.00 rc build 1733 version...most of the time aol email opens without a hitch, although buddy lists and right hand side toolbars don't always open properly...and sometimes i have to reload pages because either it takes too long, compared to firefox 3.5.2, loads only parts of web pages, or doesn't load at all...but these situations don't happen often....another thing about opera 10 rc so far i have issues with the "voice" component of opera (which i use for text-to-speech purposes). I also have the opera icon in startup menu, so opera opens when i turn the computer on...and so far opera has crashed every time i turn on the computer, with opera 10rc/previous builds as well...apparently this might be due to having the opera voice component installed, but i don't know...
however, besides these minor issues, i have used opera 10 since alpha, possibly 70-80% of the time, and firefox only as a backup, and internet explorer only to use "Microsoft Update" site.
I have to say Opera 10 so far is "unique" compared to other browsers, and I cant find a way to move toolbars around. You can change them to left, right, top, bottom. But if I would like the tabs toolbar below the address bar, or move other toolbars up or down IN RELATION TO other toolbars, it would very helpful, rather than just up, down, left,right OF THE BROWSER WINDOW. Besides these minor gripes, Opera 10 so far for me is very customizable, not exactly easy to master (so many other options and preferences can take weeks to figure out the whole application)..
I do love the Opera voice component, however insufficent it may be, because text to speech is very important to me. I also haven't figured out the bittorrent component yet, or the mail application, and Opera Unite is another component that is yet unfinished, but makes it an ALMOST all-in-one browser...but so far "for me" anyway, sort of a love-hate thing...I hate the problems it gives me, but I still love it.