Depending on your comfort level with the guts of OSX, there are some things you can do.
First of all, turn of daemons you aren't using. If you don't use ssh, apache, etc, turn them off.
Second, you can manually remove languages, printers, video card drivers, and other system related items you don't need.
This will add a hint of speed, and some space.
Carefully check your login items. Remove anything which you do not want to startup explicitly. Look for legacy processes via top or ps -ax. Fruit Menu leaves a stain long after you delete it, as do many other programs. Kill/delete as necessary, but with care. If you don't know what it is, don't delete it!
After these steps are completed, analyze what may be bogging things down (in OSX it is not likely to de your disk). Boot verbose (cmd-v at startup), and watch what the computer is telling you...are you loading Airport without an Airport card? Are you using AppleTalk services but not sharing via AppleTalk?
Also, an fsck -y can clear up some odd slowdowns. When OSX has disk problems, it usually involves B-Tree counts, or orphaned nodes. Booting in single user mode (cmd-s at startup), and running fsck -y can reslove these issues. The OS will plod through most of them without faltering, so if you have slowdowns, this may help.
For the record:
fsck is a disk repair program. It is native to, and a part of, the OS. It will repair many problems. It is safe (it will not create any new problems). Optimizing drives under OSX is not going to yeild the benefits seen under 9. Why is there no Norton for Solaris/Linux/IRIX? Using 9 utilities on an OSX drive should be done as a last resort (not as a preventative measure). If you must using an OS9 utility, start with DiskWarrior.
