I finally got so sick of the graphics card bugs I was having that I replaced my HD4870x2 with a HD5850. It's not as powerful a card, but it's not too much of a step down and ought to run everything I have very well. In fairness it does have some advantages over the old card. I do rather covet the HD5970... but it's so far out of budget it isn't even funny.
I installed the card tonight and not ONE graphics bug or crash so far. Touch wood.
If you're wondering, the theory is that the card partially melted some months ago, probably due to poor fan management in a previous version of the driver. Asides weird graphics phenomena some games crashed the card - or occasionally it crashed just because - and intermittently I'd have to repeatedly restart the computer until the card was warm enough to function properly. It worked fine in that regard for most of winter though. Go figure.
Right. Enough of that. Any of you who are not asleep yet undoubtably know far more than I do about these things.