just taking a random guess but given by the rate and the typical style of nvidia, i'd say another month.
only guessing though. i am also waiting on the 660's review.
If TSMC can make enough of them without costing Nvidia to much. They all have to pay per wafer for 28NM products unlike the old agreement that was per working sample.
Given the success and demand of the 670, I guess they're gonna cash in on it (670) for the time being. Once the demand goes down a bit...or if AMD pulls one out of their sleeve...perhaps then.