For trouble free OSX computing ... I recommend these steps and apps ..
After any update .. Repair permissions: Close all files and applications on the disk you want to repair. Go to Applications/Utilities/Disk Utility and double click it. Then select your hard drive in the left panel and First Aid at the top. Then click on "Repair Permissions." It will take a few minutes.
Essential Maintenance Tools
Macaroni ... Just Set It and Forget It!
http://www.macupdate.com/info.php/id/9633
Why should you have to remember to clean up your Mac every day, every week, and every month? Shouldn't a computer be able to remember for you?
Macaroni is a tool which handles regular maintenance for Mac OS X, including the Mac OS X repair privileges process as well as Unix-style maintenance. Without Macaroni, some of these tasks normally run in the middle of the night, and don't get run unless you leave your Mac on all night. Others don't run automatically at all, and won't happen unless you remember when they're due.
Macaroni remembers the schedule for you!
Macaroni runs these maintenance tasks on a regular schedule, regardless of when your Mac is on. If a scheduled maintenance task is not run when it's normally scheduled, Macaroni automatically ensures that it's run at the next opportunity, whenever the Mac is on.
Also every month or so ....
Cache Out X
http://www.macupdate.com/info.php/id/9538
Cache Out X clears out the cache entries on your machine, helping you recover valuable disk space on your machine. Items removed include the caches in System, Users, and Library, along with the Internet Explorer download cache. Optionally clears the IE's history cache as well.
If you like to dabble ... try Cocktail instead .. however make sure you know what you're doing ..
References for above suggestions ...
Apple's Say on Maintenance Tasks
http://docs.info.apple.com/article.html?artnum=107388
Panther Maintenance Tips
http://www.macdevcenter.com/lpt/a/4400
Defragging ... Tech Tool Pro 4 is highly rated ..
For more on this topic ..
Former Senior Engineer at Mac Norton Utilities discusses Defragging
http://db.tidbits.com/getbits.acgi?tbart=07254
Apple - OS 10 Disk Optimization
http://docs.info.apple.com/article.html?artnum=25668