One of the challenges that people face in creating a Meetup is finding a space to hold it in (I think). I know this is inhibiting me from starting a Meetup here in New York.
I therefore suggest that you add an Airbnb (space booking) style functionality to the Meetup website.
This would allow people and businesses to add their spaces to a database which would be searchable by organizers and potential organizers looking for space.
I'm thinking particularly of individuals who might be able to charge for use of a room for an evening. There would be accountability because they would be dealing with the organizer or potential organizer of a Meetup who has already established a profile at Meetup. They could make their rental decision based on that.
In this economy it might even benefit folks trying to make a little extra income.
For small businesses the idea might work even better. Someone I know forwarded me an email from someone trying to rent out her art gallery for an event of some kind. These kind of spaces might benefit from the larger Meetups. As another example, some restaurants have private rooms that they always want to rent out for private parties.
July 19 2012 cc: Loosecubes