I am waiting to use my code for MPLS. Although I now have realistic expectations on my chances for GA from the presale, I'm sure I will get a decent ticket for the show somehow.
Last time 'round MPLS sold out pretty fast. But there was a trickle of tickets available at various times all the way up to the day of the show. I got my GA's by just persistently checking TM. There is always a release of extra tickets. Not a lot of them, but some. And some will be GA. It's gonna take luck... just don't give up.
I did score GA for the Denver show. I am seeing it with a friend from Denver who got shut out himself. The order went through almost instantly the second the regular sale opened. It was just dumb luck.