Revit doesn't automatically number everything. It does it for doors, windows, rooms. In Revit MEP it numbers a variety of other elements too, some of which people wish weren't because they end up generating useless warnings. A post at AUGI asked about numbering parking stalls. One suggestion was tricky and involved temporarily changing the category of the parking stall to doors so the automatic numbering would kick in. How about using the Extensions for Revit instead?
Seems to me that too many people are either unaware of the extensions that have been available for Revit for several releases now or they just don't have them installed. One of the extensions is called Element Positioning. Pardon me, lousy name for the routine, sorry. I've posted a short video showing how it works in the context of parking stalls. I've embedded it here too if you'd rather listen than watch.
[amended 5/12/10] Room and spaces are not valid elements for this tool. Neither are annotation or load elements (according to the tool's help doc). This tool got its start as an add-on for Revit Structure and was made available to the other versions.