Gizmodo has a good 'feature by feature' comparison of the software used by the iPod and Zune. Gizmodo compared features like importing music, music playback and even the music stores themselves. Here's a bit:

Music Importing: On install, the Zune automatically imports your existing iTunes database, for the most part without any hiccups. It even grabs the playlists and converts them to Zune's default playlist format. What it doesn't do is import the smart playlists, so you'll have to start all over with those. Except you can't, because there aren't any smart playlists in the Zune. In any case, the Zune should carry over the non-protected iTunes music, but if you purchased songs from the iTunes store (or any other online store) you're out of luck.

Also, you can't drag and drop stuff onto the Zune, you'll have to set up folders that it automatically monitors. Useful in one way, but kinda awkward in another, since it has to rescan all folders every time you add a new folder.

Music Store: Some of you won't care about this, *cough* file sharers *cough*, but in the realm of selection, Apple has a couple million more songs than Zune. Eventually Zune should be able to catch up, but if you want more music now, you'll have to go with Apple. However, if you're looking to buy tons and tons of music, Zune has a all-you-can-eat subscription plan to rent music for $15 a month, which is great if you want to load up your entire 30GB with songs that you don't currently own. Buying music is equally simple on both, as long as you've either already have an Apple account or a Hotmail/Xbox 360 Marketplace account.