I don't think this problem is directly related to "Snow Leopard". I actually started having the file "Save" and "Save As" problem after the Photoshop CS4 update but that may have coincidental. I Upgraded to Snow Leopard figuring a new O/S might fix file save issues.
I think I finally got it "Worked Around" and in the process found an easy, albeit annoying fix.
Annoying Fix:
Create an new Admin level user and use that to run programs that won't save (Turns out to be most of them)
Work Around: (Some already mentioned in this thread)
1- Go to PS CS4 preferences and turn off "Open GL" (This was an old Leopard + PS CS3 Fix)
2- Set PS CS4 memory usage to 50%
Those things helped PS CS4 a bit but not all of the other programs
3- Go into Applications => Font Book, highlight all of your fonts and Validate all of your fonts. Delete All of the fonts with Yellow or Red flags. Then to be sure you rebuild the library, you can do a Safe Boot, shut down and do an normal boot.
(This fixed some other programs like Safari, Firefox, MS Office, etc.and this might have actually been related to Snow Leopard)
4- A guy on another Apple Discussion thread, named Mr. Pi, posted this last work around on October 3, that seems to have fixed the problem. It involved file sharing and I will snip from his post as well as provide the link.
--- Snip ---
-1. Start by opening System Preferences
-2. Select 'Sharing' from the Internet & Wireless section
-3. From the list on the left choose 'File Sharing' and turn it off.
-4. Delete anything listed in the Shared Folders section
-5. Turn File Sharing back on
-6. Log out, then Log back in
-7. Done!!
--- End Snip ---
Here is the link to his post (It's Oct 3, about 3/4 of the way down "Mr. Pi" titled "Fixed It!"
http://discussions.apple.com/thread.jspa?threadID=2168885&start=45&tstart=0
Conclusions:
I'm Not sure about the Open GL or memory setting fixes but they helped a little. The corrupt fonts were a real hassle and those had to be fixed to run Firefox.
I think Mr. Pi struck the beast in the heart but you won't like that fix if you network several operators via a common drive. But I'm sure Apple and Adobe can get that worked out in short order now that it's been isolated.
Best of luck,
Dennis
BTW, As of 10/12/09 on that other thread, everyone is still applauding Mr. Pi's Fix so that might have been the biggest part of the problem.