waiting list

I'm thinking about using the signup module for an online class registration process, but I really need a waiting list feature when the classes reach capacity. Has anyone worked on a feature like this, for signup or anything else?

I found one mention of a wait-list feature here: http://groups.drupal.org/node/4151 but haven't stumbled across it anywhere else. Has anyone else had a need for this feature? I'm open to suggestions, or better alternatives than working with Signup, if anyone has any ideas for me.

Thanks!
Jen