Regarding music not available via Zune Pass...
I wish there was some way to see an explanation about availability when an artist/album/song can't be downloaded. As much as I love the idea of Zune Pass, I hate it when I am browsing the Marketplace and I come across music that is available but only for purchase. I know Microsoft can't control the studios or artists, but at least we could have a brief note about the reason why it can't be made available for Zune Pass (and maybe even what they outlook is for changing that). It's especially frustrating with artists that have some of their albums/songs available for Zune Pass download but not others.
And what about a way to be alerted to (or see a report of) music that has recently been enabled for Zune Pass downloads? I've been disappointed by not being able to download many things in the past, but I have no easy way of finding out if the status has changed for those items. It's easy enough to recheck on specific music, but I want to see a list of ALL music enabled for download in the last week (or something to that effect). I don't want to have to remember to check Led Zeppelin or The Beatles or anything Disney (for my kids, I promise!) every couple months to see if things have changed. Or another angle might be to have the Zune software allow users to flag specific artists/albums/songs for later follow-up (either to purchase or hopefully download with Zune Pass).
As many others have pointed out, Zune Pass can be a great way to experience new music or indulge in nostalgia without having to buy. I certainly don't want to buy "U Can't Touch This" by MC Hammer, but I love that I can just grab stuff like that (legally!) when I'm in a flashback mood. Or I can download 30 albums of Christmas music and then ditch it all when the season's over. Especially for us old fogies who had their main music collection on pre-CD media formats, Zune Pass is a nice option to have. Now if Microsoft would just enhance the usability a bit more...