Can I install 16GB RAM on quad-core MacBook Pro?
According to Apple the answer is no, but OWC has tested it and found that there are no issues putting 16GB (2x8GB) in the latest generation MacBook Pro. The upgrade doesn't come cheap, though - at this time 2x8GB modules will set you back $1599.

http://eshop.macsales.com/item/Other%20World%20Computing/1333DDR3S16P/