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.