It seems I'll have to wait for Opera 11 for extension support. I hope it's finally added in that version.
Yes, Opera is a kind of "one size fits all" deal, and feature packed, but if you use for example a certain social application a lot, it sure helps to have integrated support for it, and you can't expect Opera to be able to meet all demands. We're different users with different needs, and browsers should be streamlined for those needs, so that a user will have neither too much nor too little in a browser. This is a critical point I think Opera has been missing for a long time now.