Here are some things that use Playdar. The search and hAudio demos are hosted on playdar.org and aren't very sexy. The other demos are separate websites, and are much nicer.
Simple search interface that displays all results after polling completes.
Simple demo that shows the built-in hAudio parsing from playdar.js. Imagine the ugly red/green boxes were sexy buttons.
Playlist player that can import playlists from Last.fm, XSPF, podcasts. Also imports album listings and can generate a playlist by combining two Last.fm profiles.
A web-based Playdar player that imports your Last.fm library.
Spiffdar allows you to view and resolve XSPF playlists using Playdar. Has a handy list of top genre playlists from Last.fm webservices.
A bookmarklet for various sites that makes it easy to turn webpages into playlists, then send them to Playlick or Spiffdar.