I tried installing an antenna in my attic without any luck. I didn't want to mount it on my roof, so I just installed it off my back deck about 10' off the ground. Then I routed the 50' cable under my deck, through the basement, through the crawl space, and then up through the livingroom floor.
I have some trees starting about 200' back from the antenna, but the lot slopes down, so it seems to be a good spot for it. I'm also only 13 miles from the towers, and they're all in the same direction, so that definitely helps. BTW I have the
CM4228 antenna. The antenna plus the mast were about $85 shipped.
Also, as long as you have good signal strength, OTA is the best quality HD broadcast you can get. It seems that in some markets cable TV doesn't compress the HD signal much, but in other markets they compress the crap out of it, making it look bad. I can definitely tell the difference between OTA HD and the DirecTV I used to have. I ran both for a month or two while I was setting up my HTPC, so I was able to do some back-to-back comparisons of the exact same programs.