When you delete apps you can use something like App Cleaner to make sure it gets rid of all of the extra .plist files that get scattered around and stuff. Other than that you can leave it on at night so it can run its maintenance routines, etc.

I did an erase and install after not doing one for about 4 years, including a Migration Assistant move between two different computers and only noticed marginal improvements in speed. It just cleared out a lot of old things I had installed over the years and then removed, including some web server stuff that was being launched at every boot and would have slowed it down a bit.

Keep %5 OR 5GB of your harddrive free, whichever is bigger.

Check software update to make sure you’re running the latest software.

Also, make sure you have enough ram for what your trying to do. Macs really don’t have the same flaws as PC’s in the sense that you are talking about.

I have a desktop and a laptop. I use both professionally that is to say I have photoshop, aftereffects, illustrator, and final cut. these are professional strength programs, open with mail, chat and the web. I might go days with out restarting and not have a single bit of degradation in performance.

In addition to that if you are working on photos or video or the like. Keep your applications on your main hard drive, separate from you source material and your scratch disks. That will speed things up.

An occasional reformatting may be required. Download all of your info to an external drive, defrag, and re-install. Lots of times it is just clutter.

@dannyc – Good idea.

You can also use SuperDuper for free. It makes a perfect copy, just in case you want or need to get some stuff back.

How do I defrag on a mac?

You don’t. It defrags itself every time you open or save a file.

dannyc probably meant to erase and install. Which isn’t really necessary either for most people.

I actually have never done that for either of my computers.

I moved from a stuffed 80GB harddrive to a spacious 320GB and used superduper to move all my files, not only did the extra space speed things up, the move cleaned a lot of hard to reach places, metaphorically.

@willbrawn Whiping the OS and starting over doesn’t help. Why? Because after a whipe, all the data is still present on the hard disk, it just doesn’t show up and gets overwritten with new data when it needs to. Writing over old data is slower then just all zero’s (blank).

That’s why all computers get slower when the harddisk is (or once was) near full. The virtual memory constandly needs to write over old data, which is when you often defrag likely contain tiny disk errors.

The best solution: Whipe the entire harddisk by writing it with zero’s (7x or more).
The other solution: Whipe free space with zero’s (7x or more).
http://docs.info.apple.com/article.html?path=DiskUtility/10.5/en/duh1010.html

iTool has most system maintenance features and cleaning you could ever need. Moreover, it unlocks some additional hidden settings or visual preferences in Leopard. Check it out and see if you like it.