I LOVE MINE! I have a USB to IDE adapter. Got it from e-mart.com . I put it in the car on the way to work...pop it out and bring it into the office. Back in the car...then back to my desktop. Great portability!!
USB 1.0 (which is what mine is) is more than fast enough to play mp3s. You run them from the usb drive. Most newer usb drives are usb 2.0 which are 40 times faster than 1.0 and like 10 times faster than firewire. 1.0 vs 2.0 wont make a difference when playing mp3s...just when transfering a massive amount of files. USB 2.0 requires a usb 2.0 card in your computer but are backwards compatible. Hence you can use a 2.0 drive on a 1.0 card...but you only get 1.0 speeds.
As far as taking a beating, I understand that they are basically what i have...a hard drive and an ide to usb adapter. Hence, they will take just as good a beating as a regular hd. I put a 40 gig quantum in mine. It takes a good beating considering the truck im driving and the fact that i just throw it in my bag on and drop that on my desk every day.
ONE NOTE: Most of them require an external power source. The cheaper ones at least. Bestbuy is carrying a new brand STORIX which dont require and external power source and are USB 2.0. Considering the great usage I am getting out of my current one Im probably gonna get a second.
Here are a couple that Im looking at: check pricewatch for best rates. The second one by buslink can be found MUCH cheaper.