Very cool stuff. I always wanted to pick up PIC embedded programming, but always had too many other things in Python to play with. Now it seems I wouldn't have to learn a new language. I wonder how well this stacks up with hand written PIC code.
If you want to write production embedded code, you have two choices: C and assembly. That's the result of my extensive research, anyway: gcj doesn't work, the AVR forth implementation uses too much flash and can brick your chip at runtime (for other reasons), etc.
Definitely keep in mind that this thing needs to be connected to a host PC over USB to do anything. You are not actually programming the PIC and then having it do stuff on it's own. The pyMCU folks probably program the PIC in C or BASIC, and you would just be using the provided firmware.