Use Zune Marketplace Backend with MP3Tag
"Given that the current (and past) Zune software lacks any decent metadata editing I've been using Mp3tag to adjust the various tags as well as grab album art. One cool feature of Mp3tag is that you can look up album information from a variety of online sources, most notably Amazon. From there you can grab track listings and album art to help flush out your metadata.Only problem is that sometimes the Zune Marketplace files an album differently than Amazon[...]. After poking around with Mp3tag's extensible "web sources framework" and using Fiddler to watch the HTTP traffic to and from zune.net I cobbled together a Zune source that will pull down the exact album information as listed on the Marketplace as well as the album art."
Shawn Oster points out how easy it is to hook the backend of the Zune marketplace into MP3Tag to get properly tagged and recognized files. He also points out that this could be helpful in getting Social to recognize the songs you play (though I'm not convinced of his argument that Social takes the album metadata from your computer--I'm pretty sure that comes from their servers).
He brings up another cool tidbit: "zune.net just made their 800x800 album art available via the back-end service I'm using so now you can grab full 800x800 album art even on tracks you didn't purchase directly from the Marketplace. Just download Marketplace.zip and extract the single Marketplace.src into your %appdata%Mp3tagdatasources folder and you'll be rocking! I'd also suggest you download the very latest beta of Mp3tag because the tag sources (what Marketplace plugs into) dialog is much easier to figure out for first timers, plus I always include the artist in the track listing and version 2.39n supports splitting this into the correct tags."