Essentially my 5G iPod was cutting tracks off and generally misbehaving. So I did the following:

1) Use Diskwarrior - heavy directory fragmentation which it fixed;

2) Use iDefrag - some fragmentation but it kept halting as it couldn't move files;

3) Try to write out drive with Disk Utility - got a warning from DU so gave up before I started;

4) Completely restored using iTunes;

5) Reran Diskwarrior - still heavy directory fragmentation;

6) Reran iDefrag, still fragmentation although limited to two bands;

The iPod is much quicker to traverse menus and no more track skipping.

My question is this - is defragging worth it or does the heat generated by the process kill the drive and make it a self-defeating process. Anyone have any metrics/ figures? Clearly it's a bad idea for solid state drives like the nano & touch.