I have never defragged my slot-loading iMac (40GB), and I am suffering. I can't import more than about 15 seconds in iMovie 2 (let alone 3) without dropping frames. When the computer was new, I imported (and exported) 2 x 1 hour tapes in one go each, with no dropped frames. (that was the only time my hard drive got within 5GB of full)

I was also recently using an older, slower, but recently reformatted iMac, and was amazed at how fast it booted and how quickly applications loaded after logging in.

There aren't any free defrag utilities for mac, apart from a borrowed external harddrive, are there?

I agree. Especially for older Macs. When the drive on my G4/466 gets badly fragmented the whole computer runs very poorly.

Also when trying to work with audio files in applications such as Cubase SX, you can really see the loss of performance.

I still use Norton SpeedDisk to defrag (booting into OS 9) but it's getting long-in-the-tooth, and often has a hard time dealing with the thousands of files on a typical OS X hard drive.

The built in defragging isn't worth a hoot!

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G4/466, 1 GB, Mac OS X 10.3.6