Many of these questions have already been answered in this thread already which is probably why no one has responded. The "Search This Thread" feature of the site is your friend... but I'll be your friend too and answer your questions.
Yes, you can pick up HD channels over the air using this TV but you have to use an antenna to pick them up and your antenna has to be in the range of the broadcasting area of an HD broadcaster. There are plenty of sites out there that you can find more info about this but I'll start you here: http://www.antennaweb.org/aw/welcome.aspx
The other HD option is to utilize the QAM tuner on your TV and pick up unencrypted HD channels from your cable provider. I am paying 13 bucks a month for "basic" channels from my cable provider and still pick up around 8-10 HD channels (and about 200 digital music channels). All this requires is that you plug your cable directly into your TV and perform an auto scan on the TV to pick up the digital channels.
I personally have not used the calibration settings from CNET.com so I can't comment.
SD is underwhelming on any HD set, pure and simple. If you're expecting a pile of crap to somehow look like a work of art then you are expecting just a little too much. There are ways to diminish the crappiness of crappy SD tv on this TV but you can't expect miracles. You can search earlier in the thread for my personal settings on how I've reduced the artifacts of SD content on the internal tuner. My wife used to complain about the appearance but now she can't really even tell that it is bad anymore. I simply don't watch SD on my TV anymore. I either watch HD channels or watch movies over the HTPC... I use it for nothing else.
Hope that helps you out. But don't be afraid to actually search this thread for more detailed information.