There is now a new version 2010.06.26 of MediaBox Media Center available in extras-testing for N900 and extras for N800 and N810.
It’s somewhat a small premiere. 
As far as I know, MediaBox is the first 3rd party media player on the N900 to support the Maemo MAFW framework for media playback.
MediaBox is also the first media player written in Python to use MAFW for playback. Of course my code for using MAFW is open for anyone to use in their Python programs.
Using MAFW on the N900 has some benefits. For instance, audio will play in silent mode and doesn’t stutter while locking the screen. And you are able to control the volume with the hardware keys while the screen is locked (this requires Maemo5 PR 1.2).
In case you prefer mplayer over MAFW, and have mplayer installed on your device, you can use it as media backend as well. Or just use plain GStreamer as before. The backend to use is configurable per media type.
On the N8x0, the available backends are OSSO Media Server (the predecessor of MAFW), mplayer, and GStreamer.
How do you normally get music onto your device? Now you can browse your UPnP media shares and download whole folders with their media contents onto the device. YouTube videos can be copied to the device, too, and MediaBox manages all this with the new download manager component.
There have also been made some (a lot) performance improvements in the new version, and the handy sleep timer from the 0.96.x series of MediaBox is back.
Enjoy, and please don’t forget to vote for the package if you’re using it from extras-testing on the N900!
