I'm finding the opposite. Fast, only lags when it runs into the N900s 256MB memory limit, never crashes. It's also extremely compatible with today's internet.

The only things I'm missing are the ability to play videos, the lack of automatic capitalisation and the inability to save sessions. The latter would mitigate the fact that Opera Mobile 11 won't sleep properly and burns battery when not used

There was some talk about getting Opera 12 to run via MeeCoLay.