Planning a conference is really tough. You have to guess how many people will sign up, and guessing accurately is really important.
On one hand, you can’t rent a 900 person facility if only 300 people are going to show up (unless you like losing money). On the other hand, you really want to be able to accomodate everyone who is interested.
RailsConf 2006 initially opened registration with a capacity of 400. That sold out in about a week, which shows that their original guess was way too low. But who would have known?
It appears that they renegotiated with the hotel and were able to secure an additional 150 seats. When they reopened registration those seats sold out in less than 24 hours! This really makes me wonder how many people would have signed up if the capacity had been there.
All is not lost, however. They still have openings left at the Canada on Rails conference. Many of the top Rails developers and authors are going to be there (including DHH himself). Go check it out!