If you go through the schedule now, you can check how crowded each talk is going to be.
If you see a warning sign next to a talk, it means that we expect that the attendance of the talk will be higher than the room allows. If you were planning to attend that talk, you might want to have an alternative ready in case things go bad and you don't make it into the room.
We are doing this estimate through the number of "likes" each talk has received (plus some complicated and uninteresting heuristics), so it is updated in real-time as people go through the schedule and like/dislike talks. We will revisit the heuristics to further tune them in the next days.
If you are really curious about the raw numbers, on each talk page you will find the raw estimate of attendance. I believe most speakers will be very curious about it... For instance, if you visit the page of PyPy in production you can see that the current estimate of attendance is currently 94 people. Not bad!
The schedule was made taking in full account the results of the community voting. This means that we expect most of it to be sound with respect to room sizes.
Nonetheless, we are ready to do last-minute changes to allow everybody enjoy the talks they would like to follow. This basically means that:
Now it's the perfect time for you to go through the schedule and "like" the talks you like most. Not only you will help refining the estimate of attendance, but you will also end up with a nice printable "My Schedule" to bring with you!