SusieMC wrote:
http://support.apple.com/...35?viewlocale=en_US#faq5

Apparently you can, but it will wipe your music every time you do it.

Question: I have a computer at home and one at work. Can I update my iPod music collection from more than one computer?
Answer: Yes. When you first connect iPod to your computer, iPod recognizes that computer as its "home" computer. Each time you connect, iPod automatically downloads the music library stored on it. When you connect iPod to a different computer, iTunes will inform you that iPod is linked to a different iTunes library and will ask whether you wish to erase iPod's contents and sync with the new computer's library. If you will be connecting to multiple computers frequently, configure your iPod to manually manage music. This will allow you to selectively drag songs, albums, or playlists from the second computer to your iPod without compromising the existing music.

Synchronization generally occurs only in one direction, from your computer to your iPod. This means you typically cannot transfer music, automatically or manually, from your iPod to a computer, and you cannot use iPod to copy a music library from one computer to another. An exception to this is the transfer purchases feature which allows you to restore purchased iTunes content to your computer from your iPod. Additionally, if you legally are allowed to copy music or other media files, you can configure your iPod as a storage drive to move media files.

(bolded the important part)

As long as you select that you want to manually manage the music on your ipod, it won't wipe it out every time you hook it up.  Also, it asks you before it wipes it out, so you always have the option of clicking "No".