Problem ~ You've upgraded from Windows XP or Vista to Windows 7. Windows 7 Upgrade adviser tells you to uninstall iTunes and re-install after the upgrade. You figure you can just sync your iPod and get all you music afterwards, but iTunes gives just two options: 1) sync the current (empty) library with the iPod -- destroying everything on it, or 2) transferring the iPod songs to the library with the rather ominous line "all of your iTunes store purchases..." If you are like me, then a LOT of you music did not come from iTunes. The problem with Apple (sorry for the rant), is that they have this attitude that they know best, and the world revolves around them (why would you purchase anything outside of iTunes??), and their iPod transfer of music process absolutely sucks.
Assumptions ~ You have your iTunes music folder backed up somewhere (external drive or, after the upgrade, it may be in the windows.old folder).