I'm sorry I have to disagree with all of you (apart from forum2233) as I have the same problem.
Stop blaming Windows please that is not the issue. On the same system that Opera is giving an 'Out of Memory' error I also have Firefox, Chrome and even IE - Yes that's right all of the other browsers are working just fine.
Stop pointing the finger and realise that there is a problem with Opera - yes that's right, as difficult as is is to believe here in forums.opera.com land it still has problems. Stop burying your heads in the sand and please stop thinking it's perfect. Stop blaming the operating system even though it's Windows (lol, oh how funny we all use Linux here smarmy land) and deal with the problem at hand.
Mr. Lando242 with your 1013 posts, if you have Opera with over 400 tabs open and everything is running for weeks then you're a ....