Recently, I had a problem with my iPod not being recognized in iTunes, while it was connected to my computer and uploading .mp3s. I kept getting the Do Not Disconnect message on my iPod. After restarting my computer and going back into iTunes, it still wasn't recognizing my iPod. I thought I was in trouble at this point.
Fortunately, I was able to turn off the Do Not Disconnect message from my IPod, by resetting it while keeping all my files intact. Here's how: To reset iPod (for use during troubleshooting), press and hold the Menu and Select buttons simultaneously for about 6 seconds, until the Apple logo appears.
Another problem I encounter fairly frequently while walking or running with my 20GB iPod is that it will just freeze up and stop playing. The song or podcast I'm listening to at the time will just stop, and the buttons on the iPod will not work when you press them. To get the iPod working again, I've found that you can either plug it back into your computer, or if your not around your computer try keeping the iPod still, toggle the hold switch on and off once or twice, then unplug the headphone jack going into the iPod, now plug it back in, and then reset your iPod (hold the Menu and Select buttons simultaneously for about 6 to 10 seconds).