I have a similar query myself. But I'm not turning up many hard facts via google, so thought it might be worthwhile posting my stats here. With enough posts, we may get an idea of how people's systems are running...
So, my AMD64 3000+ runs at 58 ~ 60 C. I thought this was pretty hot, but haven't had any stability issues whatsoever.
I have learnt that the maximum temp as quoted by AMD is the "maximum die temperature". I don't know if this was an intended pun, but at this temperature the chip will be damaged. I don't know how close to this temp the chip will continue to operate correctly and safely.
However, here is an informative link with worrying implications:Safe CPU Temp
The die of the chip may be a lot
hotter than your temperature gauge reports.