Mounting .DMG disk images has been getting slower and slower on my 10.2.6 machine, to the point where it took at least 15 seconds to open any DMG. I figured the OS was caching mounted volumes or something, and searching a bloated cache was causing the slowdown. Sure enough, I sudo rm'd the Library/Caches directories from ~, /, and /System, restarted, and now DMG mounts are back to a couple of seconds.
[robg adds: The actual command to do this would be:
% sudo rm -r ~/Library/Caches /Library/Caches /System/Library/CachesYou won't permanently hurt anything by removing the cache files, but you may notice that it takes longer to open large directories (for example) while the cache files are rebuilt.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030918144014566