I was looking for a way to share iPhoto and iTunes data between two accounts on the same Mac. There are a variety of old solutions that involve adding both users to the same group (like “staff”) and then changing the group and permissions on the files to be read/write for the group. For me (using Mac OS X 10.4.10 and iPhoto 6.0.6) this mostly works, but various files get rewritten with new ownership and the wrong group on each iPhoto launch. I worry that new files will not have the proper permissions and this will hose things down the line.
I finally found this technique using Tiger ACLs that looks pretty slick. I have yet to try it, but it should work.
Update: I tried it out and it seems to work. Sweet!