KNTV-DT has been fine here every time I've watched it. It was fine for Jay Leno last night on 12.1 (11.1). I'm receiving the signal off the air.
In response to "mkmpanic", using a Channel Master 4228 for UHF, where all of the stations except KNTV transmit, and a single Wingard yagi for KNTV on VHF, I'm able to get 19 digital stations here in San Francisco. Some viewers, those who can get the Sacramento stations, can get even more.
You should have no trouble picking up the stations from Sutro Tower, Mt. San Bruno and the East Bay hills with something like the 4228 in Redwood City. You might even get KNTV from Loma Prieta. The last time I checked, Frys had the CM4228 in stock.
For a complete list of stations that are on the air in Northern California, check out the list I've put together on my website. You'll find that list and a lot more at: http://www.choisser.com/broadcst.html