Best practices for creating unique IDs
Quarrelsome: Do you have security concerns besides someone guessing the id?
I always figured you just make sure you only allow authenticated users to edit/view the data they are authenticated to see.I always figured people used GUIDs over ids to avoid the performance implications of re-pinging the database to get the new id. 
I would be cautious of creating my own GUID generation though. I'd assume that the db's GUID implementation is probably WAY better than anything one can hack together within a short time-frame.I'm an auto-increment man (if I can get away with it). :)