But what else to select...

What I do with my 10Gig iPod is have two smart playlists. One of these selects 2Gigs of my most recently added music. The other selects 7Gigs of my most often played music. Both are automatically synced to the iPod whenever I plug it in. The spare gig (600Megs actually) is used for spur of the moment stuff I decide I want to listen to and file taxi purposes. Although this isn't as good as having everything I own always available it does a great job of keeping me from ever having to worry about what to put on the iPod.

From Roger's comment it sounds like their Music Manager tool will allow you to do something similar.

-Mike