One of the earlier demos (about a year old and unfinished) : http://niiden.com/orbisyn/ :) has a virtual MIDI keyboard, to which you can connect a MIDI synth if you have Java. It isn't exactly native support, and it's very unpredictable, but it's something that can be used meanwhile.

However, the Device API should allow access to external inputs, such as microphones and MIDI controllers, so it's coming along!