Might want to make it known that a deposit is required when making reservations.. That kind of caught me off guard as I've never had to do so for a convention before with a credit/debit card reservation 
Transaction Type: DIRECTDEBIT
Posting Date: 04/10/2006
Transaction Description: DIRECTDEBIT/MC-HILTON HOTEL ADV DEP HOUSTON
Amount: -$115.83
I'm coming the day before the con starts, might be less for those coming the day of the con, I'm not really sure though..
Yeah, I figure thats the reason, it's just the first convention hotel I've gone to that I've had do this so I thought maybe it should be mentioned on the hotel page
Question.....will they return the deposit to us afterward?.... Is my first time to pay deposit to reserve a room too.....
Usually deposits go towards paying off the room and they aren't refunded.
That's really sucks
You won't be loosing that money, it'll go towards paying off your room...
I hope so
Anyway, thanks Keely and Bishie-san 
I work at a different hotel... but, the way we work it is:
we capture the entire stay (place a hold) plus $12. When you check out, we log the entire transaction as complete.
When the computer system gets updated at 3am, all credit card transactions for the day are completed. Any reversals, or any holds that need to be released, are also done at that time.