Your registration goes into a queue as regulardave says. HOWEVER, you lose your place in that queue if you close the tournament window before you get your confirmation of registration back.
The daily freeroll sat to the $50K fills up quicker than any tournament on PS. You have to get in right away and leave the tournament window open until the registration is acknowledged.
Come to think of it, that donkament would be a perfect holiday starter for me tomorrow morning...