Wow, might actually know what I am talking about on this one.

Been a DirecTV customer since 1995 or so. Have had HD for a few years now.
Ok, here is the deal...
No local HD via DirecTV here in the triangle (yet?). DirecTV does offer some HD content, but not locals (yet?). I think they have worked a deal with at least CBS that for the CBS "Owned and Operated" markets, that they will allow you to get the national HD feed. I am pretty sure this does not include our area. I probably can find a URL for the details on this, but like I said I am pretty sure it is not for our area yet, so I haven't dug very deep.
Rumors abound regarding additional HD content on DirecTV including locals. DirecTV (now owned by Rupert Murdoch/News Corp) has a new Sat that is set to launch soon. It could provide the ability for HD locals in some larger markets. Nobody knows for sure. HD requires more sat bandwidth than regular non-HD, sat bandwidth is precious, etc. You see the problem here.
Dish currently probably provides slightly more HD than DirecTV, but no locals as well. I expect that with the new owners they are going to put more HD on DirecTV to directly battle Dish. There is also an upstart sat provider that I think is actually owned by a large cable company called “Voom”. Tons of HD content, but again, no locals (yet). Jury is out on “Voom” right now.
Regarding local reception...
A HD DirecTV receiver will be able to accept the OTA (over the air) signal via a built in tuner. But that is not compatible with what Time Warner provides. Basically for the near future, you have to use their box to decode the signal. If you want to put up an antenna you could use the DirecTV box. Even then, it depends upon where you live, etc. regarding the type of antenna you need, etc. In other words, the antenna solution is going to be much more complicated than your current cable setup. As much as I love DirecTV and hate cable, I would say stick to cable if you want local HD.
To add some FUD to this, the entire copy protection thing is still not 100% worked out with regards to HD broadcasts. This alone is a topic that would take pages to jump into. Basically "things are still a changing".
One extra that you didn't mention. Don't know if you have a TiVo or if you ever wanted one, but DirecTV and TiVo are currently beta testing an HD PVR for DirecTV. Like above, it will also record OTA (but not via cable system).
Long term there is a new standard called "Open Cable". The idea is that when cable companies move to this standard (I think there is an FCC mandate for this) that you would be able to buy a decoder box from anyone, but that your cable company would provide you with a security card (much like DirecTV and Dish already does). When this happens (2+ years from now?) you will see more and better options than you have now.
If anyone else is curious, Email or PM me for more info.
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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.comMoney can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.