The same friend that asked me for a recommendation on a DVD player just asked me for some info on over the air HD. RIght now I've only had experience with Time Warner in Austin using their digital set top boxes (Explorer 8300HD) and now cablecards with Tivo Series 3 DVRs. I had to do a little research but found this useful article on CNET's site: http://www.cnet.com/4520-7874_1-5108854-1.html?tag=lnav
Basically there are a few sites you can use to tweak your antenna setup to get just the right direction. Something I learned here is that over the air digital signals won't suffer from ghosting/flicker (makes sense) but may just drop out all together.
Does anyone have data on if over the air is higher quality because there's no compression to deal with? Does it totally remove the blockiness of a digital cable box's transmission?