I'm current running VMC accessed exclusively through my xbox 360 extender. I have TVersity (mainly so that I can watch all my anime that needs to be transcoded so the xbox can play it) and PlayOn (for Hulu, etc.). I've been using vmcPlayIt, but it is sometimes wonky. It connects to PlayOn stuff, but not TVersity. And it's free. The UI was recently updated too, so that's nice.
TubeCore can connect to both in one easy to access spot. I don't know if it's worth the $20 cost though. I can still get to my TVersity stuff through other (far uglier, yet free) separate means, or just drop to the xbox dashboard. Was wondering if anyone had tried tubeCore and had any comments or opinions, particularly regarding the UI. I'll be upgrading to Windows 7 Ultimate in a couple weeks (thank you Windows 7 Launch Party) and want to get everything set up and running smooth before the official Windows 7 release on the 22nd. TubeCore does not work with Win7 now apparently, but claims it will at launch.