A few days ago we covered a problem where some CS5 applications were bringing up an "unexpected quit" error when they were shut down by the user. Some other folks are having issues on the opposite side of the spectrum, where Photoshop CS5 is unexpectedly quitting on launch.
The problems seem to be focused around how Photoshop and the system are managing fonts, particularly MultipleMaster fonts, of which some may have been installed by Adobe applications.
Search through the font directories in the system library, the global library, and the user library to see if any fonts with "MM" in their name are present, and remove them from these folders. In particular, look for fonts that are similar to some of the core system fonts that Apple uses, which include the following: Courier, Geneva, Helvetica, Monaco, Symbol, Times, and Zapf Dingbats.
Apparently Adobe is aware of an incompatibility with MultipleMaster fonts, and is in the process of developing a fix for it, but meanwhile disabling the fonts should help some users.
Beyond MultipleMaster fonts, you should check your fonts for both proper read/write access and for other miscellaneous errors.
All of the fonts in the System and Global libraries should have the user "system" as the owner with read and write access, and "admin" or "wheel" as the group, with both the group and "everyone" having read-only access. The real key here is that all users should be able to at least read these documents. The fonts in a particular user's library should at least have read access by the respective user, though that username should be the owner of the font file, and have both read and write access.
Beyond permissions, you can perform font-related maintenance using a utility like OnyX to clear the font caches for the user (this can also be done by booting into Safe Mode). Additionally, use Font Book to run a verification routine on all installed fonts, and resolve duplicate fonts that may reside in different directories.