Okay, for the record, here is my experience from this afternoon:

I declared $1076 worth of goods (applicable limit of $800). My colleague declared $935 of goods (also $800 limit) and over his alcohol limit with 17 bottles of wine (i.e. 15 over). We were both waved right through.

Surely at some point they'll charge you, but I don't know at what point that is and whether they can do it up there or have to send you down. But there does seem to be an emphasis on speed of processing at those desks.