Defrag Mac??

In normal usage, OS X is pretty good about cleaning up the disk after itself where files are less than 20MB in size. So the average user doesn't have to defrag manually.

The only caveat is that if you do a lot of video work where files can be several GBs and being regularly written/deleted, then you may want to look into getting a disk warrior type app that will defrag for you.

 

Doesn't usually need it. OS X defrags automatically over a certain file size (30MB or summit). Just leave it on (not in sleep) overnight a few nights, and it will do it's stuff in your absence!
Welcome to the world of Apple - really well built software!

If you do need to Defrag (which you may after a few year's I guess) there are programs out there, but I wouldn't reccoommend it unless you are actually noticing disk reading slows down! Here is one that Apple sell, and sounds pretty good, but as you can see from reading that page, it's not needed for most people!

 

I could be wrong, but I've used DiskWarrior before, and I believe it optimizes the HFS+ directory structure, not the file blocks. I don't think it is as disk defrager, per se.