I like having this Feature Request and Suggestion thread going.
My suggestion for Zune 5.0 software: Add a column on the Zune software (similar to the device icon to see which songs are synced) that shows which songs are owned and which aren't.
The reason: we get 10 credits per month, but rarely does an album have exactly 10 songs. Often I need to get the rest of the album the following month, but I don't always know which tracks I've already used credits on. This should be a simple, convenient fix for this problem.
Thanks!