Actually, I know what caused this or at least why I suddenly got an error.

My g drive was formatted as FAT.  I had about 200 megs free on it and used this as my temporary internet location. Fine.

Problem is, as poser (ok, the OS) was writing out all these temp files (about 8000) of them, well FAT drives don't compress small files too well or at all, thus even though it was technically about 2 megs... it was taking up apparently 200+ megs of space on the drive for these files... the drive ran out of space, poser died. I had noticed prior to this alot of missing icons for items and their folders wouldn't open in the library.

I formatted the drive now as NTFS and going to watch a bit. The library items have come back.

This is a very very weird problem and obviously deeper than simply temp xml files getting written or not written.

Ok, so it's not Poser.

It's not the programmers specifically doing anything wrong. 

But I can't pin this on the OS either.... and it seems to me the newer technology here is Adobe Flex and I'd be curious if they've dug into this a bit since... hey...  whose the new guy on the bench in this mix? Not Poser. Not Windows or OSX. That leaves only one choice :)