UPDATED: Track Down Purchases v2.2
Track Down Purchases v2.2 will examine each track in the entire iTunes libraryor a selection of tracksfor items purchased from the iTunes Store (audio, video, and books) and then sort them by either the purchaser's name or account ID into discrete playlists, eg: "Purchased by Tom Ryan" or "Purchased by tomryan@email.com".
This latest version changes the name of each playlist created (prefixing it with "Purchased by") so that they'll sort together and also fixes an issue with misreading account ID data that produced garbled text in the playlist names.
More info and download here.