I set up my converter box for digital TV reception today, in the wake of the exile of the television back to my basement where it belongs. The good news is that a number of channels, including channels 4 (CBS), 7 (ABC), 9 (NBC), and 31 (Fox) are coming in clearly with powered antenna, as do a couple of Spanish language channels. The bad news is that Channels 6 and 12 (PBC) and 20 (formerly UPN and now NBC with different programming apparently), don't.
Encouragingly, the power of the broadcast transmissions for all or most of these stations is scheduled to increase dramatically on February 17, 2009, about six weeks from now, when analog television transmissions are discontinued. Antenna web tells you which channels you should be able to get from which directions and what distance, although one has to take care to opt out of the advertising options before getting a customized report.
Some interesting technical background can be found here (Power Point).