Just picked up this beauty without the microphone for $15. I got it for two reasons: ability to copy MP3's straight to the Hard Drive through a LAN cable, and ability to transfer JPG's and have a picture slideshow.
It's impressed me, I'll say that! The media player is much better than that of the Xbox standard, still not great but much better. Copying mp3's is incredibly easy, I thought I'd have to do all this configuration crap but it wasn't nessecary. The cool thing is that it initially copies them as Mp3's, so it doesn't change them to WMAs, so it's quick. Unforunately, only Music Mixer can run them then, but there's an option to convert them to proper Soundtracks, which takes a while but allows you to play the music in games and have them on the dashboard etc. This is great, because as most of us know, the dvdrom drives don't usually read burnt cd's. So it's great for getting your collection on to your xbox.
Also, for jpg's it's pretty damn cool. It would be good being able to rotate pics and stuff, but otherwise it's a nice job. Makes it great for showing pictures of your holidays taken with digi cameras to your friends, rather than using a slow-ass cd in a DVD player. Plus it's nice to load my Elisha Cuthbert picture collection onto my Xbox and view it in tv-screen goodness.
All the rest of it is pretty much crap, Karaoke and visualisations, but that's not what I bought it for :P
So yeah, if this interests you, I'd recommend picking it up for around $30 on eBay. You might get lucky like me and find one cheap without hte microphone.
I've been tempted to get it in the past, but I jsut don't use the jukebox function of the XBox enough to justify its purchase. Plus having the XBox and TV (and usually VCR) on just to play music seems like a bit of a waste of electricity.