(Sorry for the late reply, I've been
busy making games)
I don't plan to use the regular Live service but the Community Games system.
It's quite easy to submit games. The main barrier at the moment is that I don't have either an Xbox console (I do have some 360 controllers for testing on the PC, though) or the required premium account. Total cost is approximately AU$550 (US$350), so I don't want to invest in it right away.