Rails - Jan 2006 - Enforcing Quotas?

I think I inadvertently hijacked another thread when I posted this a 
couple days ago, so I''ll try again. :)

For those who have developed apps that have different levels of account 
quotas in regards to total file upload space, how are you managing it?  
Are you keeping track of the total uploaded bytes in an Account model or 
are you using OS quota mechanisms?

Any suggestions would be appreciated.

Thanks,

Sean