OliW: No progress... It's been this way for years now, and NVIDIA have made no comment (I have also emailed them a bug report, and I tried one of these threads last year). When my card was a lot newer / had buggier drivers, it behaved more like yours - lots of temporary hangs (even when just web browsing), and it would not recover from some of the hangs.
This also seems quite similar http://www.nvnews.net/vbulletin/showthread.php?t=156372
I'm glad I haven't gone and bought a new card yet - it sounds like I could end up with exactly the same problem again. If NVIDIA can't make any response soon, I'll have little choice but to switch to ATI. I'd prefer to get a GTX560, they look like a great GPU, but I need to know it's going to work so I'm not stuck with this freezing crap again.