Looks like we have the same problems here. Only on one machine so far, but I suspect it will happen on a few others. Saving photoshop as PSD to an XServe file server. We've swapped out RAM, reinstalled CS3, run all of the utilities with the same crippling results.
Specs:Dul Core Xeon, 6GBs RAM, OS 10.5.3.
I was shocked to see that this was a rampant issue. Apple/Adobe... please!