Is there a limit to number of users that can access a folder at one time?

I haven't been able to find any information pertaining to the maximum number of users that can be collaborating in a folder at one time.  Is there a maximum number or will we never hit the threshold?  We want the ability for thousands of users to be in a folder at one time because of the scale we want to roll box.com out to users, however we want to ensure it will scale properly.