Back several months ago I tried to update my laptop to Snow Leopard (OSX 10.6).  Most things worked great, but at the end of the week when I started doing some of my reports, I noticed lots of file system problems.  The Word documents I was editing would become read-only after I saved them once.  New documents I created would be read-only.  As I got to digging, I found that any files I created on the file server were being created with empty permissions (as viewed from my laptop), and read-only permissions (via the checkbox) as viewed from the Windows side.  I found lots of people having the same problem with no real workaround.  I noticed the permissions would fix when I viewed them from the Finder, or when I did an ‘ls –l’ from the command line.  I restored my system back to Leopard from my backup (which was nice to have available) and waited for a fix.  Well, the fix came in the recent release of Snow Leopard 10.6.3.  I’ve updated again and everything works great.