Syncing iPod to Mac without erasing new music?

Welcome to Fluther.

Start iTunes on your computer without the iPod attached.

Find the control to enable you to perform manual sync only, and select that. (I don’t use iTunes any more, so I can’t say where that is.)

Now you can connect the iPod and only sync-in (and delete) selectively.

Or transfer purchases

I believe you need special software to take music from iPod to computer. I use Senuti. I am sure there are others as well. Ask @johnpowell, he is the mac expert.

Ah. I should have read the whole question.

If you want to put the music from the iPod onto Computer 2 without using a cable between Computer 1 and 2 or disk or flash drive transfer or “upload / download to and from ‘the Cloud’”, then the best way that I know to use the iPod as the transfer mechanism is to use CopyTrans with that.

See CopyTrans.com.

Originally this was impossible to do, an iPod could only be synced to one computer, connect to a stranger and it wanted to erase everything. I assume it was to make it more difficult to share your music. Specific software was always needed. Has this actually changed? Or am I misunderstanding the question?

Select your iPod in iTunes, click the iPod options button, and change the synchronization management mode to Manual. iTunes won’t auto-synchronize anymore, but you can now control what iTunes does when it syncs your library with your iPod