Yeah, but as far as I know it is based on a bunch of pre-sampled rythms and it doesn't
allow you to use your own creativity as much as the 909 does... or am I wrong?
Thats not correct, the MC-303 groove box is a complete drum machine, synthesizer and sequencer. The sound part is a bit boring, you can't tweak much and it always sounds nice and soft. No mean sounds whatsoever.
The drum machine part sports the same type of easy pattern programming interface as the 808/909/707, and has loads of different sounds. It has 909 samples too, although they aren't that great.
I've use the groovebox for making demos at home. You can listen to snippets of two songs, "Pacification by force" and "Turning of the soils" from my home page, http://www.regebro.nu/lennart/music.html where all electronic sounds are straight out of a MC-303. I apologize for the singing...
Tha same goes for the MC-505, btw. I don't know about the new MC-307, but its seems very similar.