Costco Auto Program - anyone tried it?

I might be buying a Prius this coming year (still haven't desided if it's right for me, but that's another topic...)

Has anyone purchased their Prius (or any other car, for that matter), using the "Costco Auto Program?" If you're not familiar w/ Costco, it's a membership warehouse store. One of the services they offer is an arrangement with some car dealers to offer "pre-negotiated member prices" on new cars. Not all makes & models are included (at least not in my area - Wash DC suburbs), but the Prius is listed as a selection.

If I go to a dealer on my own (not through Costco) and placed an order on a 2006 Prius, I assume I'd be paying MSRP. Has any one done better with the "Costco" price?

Incidentally, when I called several local Toyota dealers about ordering a 2006, they all tried to steer me toward buying a 2005 at around $500 under MSRP.