I can remember first using Microbe and being totally amazed that you could get a PDA to make music like that. It was really like having a Roland TR606 and a couple of TB303’s in your hand all at once and without having to use lots of cables to get them all working.
I’ve been playing with it quite a bit over the last few weeks and I’ve found it really useful as a very quick musical notepad. One thing that makes it really easy to get going with is that there is almost no time taken to load a song or start one as all the drum sounds are already there, and the synths can be tweaked right away. I think that kind of immediate ability to make music makes it an excellent app for when you have only a few minutes and don’t want to select instruments or samples.