I have several machines that I routinely transfer files between. After a rebuild of a PowerBook, I was unable to upload files successfully (but I could download files without issue.) The error indicated that I did not have permissions to upload. I spent a lot of time looking at owner, group and other settings between the machines, all to no avail...
Then, I realized that in the rebuild of the PowerBook, I had created a "testuser" account first, and then constructed my usual user (we'll call it "user") account. This meant that testuser had a User ID (UID) of 501, and my user account had a UID of 502. This, apparently, was a the root of my problem when transferring files between my PowerBook and all my other machines (all of which had a UID of 501 for my user accounts).
The solution, for me, was to use NetInfo Manager, found in /Applications -> Utilities:
% cd /Users
% sudo su -
% chown -R testuser testuser
% chown -R user user
After logging back in as "user," I have had no problems with network file exchanges between these various machines. It seems that keeping UIDs consistent between peers on a network may solve some annoyances!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20051022175850619