Can I update my iPod from more than one computer?

In the official company FAQ, Apple reports that:

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.

For additional information regarding using your iPod with more than one computer, please refer to "Using iPod with Multiple Computers" from the Apple Support Site.

Can I sync my computer with my iPod if I have more music on my hard drive than the iPod can hold or vice versa?

If you have more music on your computer than your iPod can accommodate, Apple's "AutoFill" feature within iTunes will select the number of songs, audiobooks, and podcasts that fit on the iPod as directed by the user or at random.

Alternately, you can configure iTunes to either only update selected playlists on the iPod or manually update by dragging-and-dropping selected playlists and songs, from within the iTunes software application, that do not exceed the storage capacity of the iPod.

If you have more music on your iPod than your computer hard drive can accommodate, you will need to configure iTunes to manually update playlists and songs. Simply import songs onto your computer, manually copy the songs onto the iPod using iTunes, delete the songs from the computer, and repeat as needed. As long as you continue to have iTunes configured to manually update playlists and songs, iTunes should not delete the songs on the iPod even though they are no longer on the computer's hard drive.

For your convenience, you should backup your music to MP3 CD, DVD, or an external hard drive before deleting them from your hard drive to avoid having to "re-rip" songs from CDs, or potentially re-purchase music online, if the iPod becomes corrupted or otherwise needs to be reset.

How long does it take to transfer a CD to the iPod?

When the first iPod was introduced, Apple bragged that it took approximately ten seconds to transfer a "ripped" CD of average length to the iPod via FireWire. USB 2.0, used by recent and current iPod models, is a bit slower, but still of comparable speed.

Also see: Which iPods can sync and charge via USB? Which iPods can sync and charge via Firewire?