Classic opening of files from Finder sometimes glitches for me - not too often, though.
But the Preview in Finder is definitely buggy - this was so smooth in 10.0.4 - and it doesn't just apply to PSD files.
Solrac - this is not the icon preview. The icons in the column view, icon view, etc. are fine, albeit 16x16 or 32x32 and resized as needed. Preview app will open PSD files natively - you simply can't edit them. And in 10.0 - 10.0.4 this functionality extended to Column view of the Finder as well... which was sweet.
In general - I'm finding this with PSDs, a number of JPEGs (can't tell why it previews some and not others yet), and *some* PDF files. I heard a rumour not long ago that the PDF preview was killed as it locked the finder on larger documents - but don't know why this would be carried over to PSD files as well - the PSD file format includes a "merged preview" layer already - 100k or so worth of the file that is essentailly a JPEG...
Don't know, but I'm going to send feedback to Apple on it... I forget about it from time to time and then it chaps me when I remember.
-jb
**edit** Sent Apple feedback - suggest others do the same and maybe it'll get fixed one of these days. Definitely a bug as I just ran through 50 or so odd files and only 2 of them showed their preview correctly. It *does* show it correctly, even on pixelated ones, if you open an info window and choose "preview" from the dropdown... so somewhere in between something's not cooking. This DOES NOT make it reappear correctly in teh finder window - but is a faster option that opening P-shop to see through the pixelation.