My first iPod was a 20 gig 4th generation mode. I used the hell out of it, until my music collection grew to well beyond 20 gigs. Also, I kept it plugged in in my car all the time, and that toasted the battery.
I now have a 120 gig video model. I love it. Have it half full, and am trying to fill the rest.
All music at 320 kbs, except for the few items that I buy from iTunes. I have NEVER had any issues with iTunes or my music library or drm. If you sync your iPod with a computer, it has the music on it from that computer. If you sync with a different computer, then it will erase your iPod. Solution: don't hook up to other computers.
If you have multiple computers, use one as your base for your iPod, or else authorize all of them and have the same music on all. Plus you can set iTunes on any computer so that it asks you before it syncs the iPod with the library on that computer so that you don't erase the content of the iPod. You can also get software to allow you to transfer stuff from your iPod to your computer if you need to do that.
Overall, no problems to speak of. When it is -20 degrees, don't leave your iPod in your car. The iPod does not like sitting at -20 degrees.
J