I'd say having random teams has its pluses and minuses. Its definitely a great way for new and unknown artists to meet others, and in addition provides an extra challenge for the experienced. On the other hand, having random teams comes with a great risk of being forced to have complete ass-hats as partners who contribute absolutely nothing and demand recognition. However, I don't think that this is the reason
Austin decided to do away with sign-ups. Nothing against Austin, but taking signups out of the Game Jam takes out a huge chunk of work load for the organizers. From what I can tell, Austin does everything on his own and as a result gets nothing but backlash when he's a little late or has the occasional mix-up or unintended exclusion or participants.
In addition to an increased workload, as I've seen in the past two Game Jams, the ratio for the number of programmers in comparison to the number of other various participant is completely lopsided. Unless I'm mistakes, a good number of people were turned away because there just weren't enough programmers to go around.
I'm not sure what to think since I don't have all the statistical data on hand nor have been in Austin's shoes and seen exactly how much trouble he has to go through organizing these things. In truth I was really hoping to be randomly placed again, but putting together a team from scratch has it kicks too.