Question

If you're only going to use it as a hard drive then it's not worth it at all--unless having a very small external hard drive is critical to you. You can get twice the capacity at half the price from a standard firewire hard drive.

You can use a hard drive cross platform as long as it's formatted in FAT 32. I have no idea how iTunes likes going cross platform though.

 

Answer

Yes, you can use the iPod between platforms as an external drive. If you have it formatted on Windows, the Mac will read it fine. If you format it with Mac OS Extended, you will need to install a program to read it on Windows like the following:

http://www.dataviz.com/products/macopener/
http://www.mediafour.com/products/

I used Mac Drive 5 for Windows and it worked perfectly. If you format your iPod as FAT32, there seems to be a 50% speed drop on the Mac side.

As far if it's worth it. (Yes / No). You can get one of those FireLite 80 GB drives for $299 at the Apple store and they are small (a little bigger than an iPod). The iPod is just one device to carry around and it does music too so it might be worth it just to use the iPod.

 

Unless you are going to use the ipod as an mp3 player, you would be better off getting a regular firewire hard drive. I just bought an 80gb one made by lacie for $129.