There really are no downsides as long as you do not mind the dish on the side of the house. I suggest NOT using Direct tv's "free" service to do the install, I would hire a qualified person to do the install and pay for it. If the dish is properly installed you should have ZERO drop outs. Especially were you are with the sat almost right over you, trees and such should be no issue.
You will need to get your internet and phone still through cable or DSL.
Plus sides are all channels are digital. Yes the channels change as fast or faster then Cables digital channels. Not sure about your area but Sat is MUCH cheaper then Cable for us, and if you have more then one house you can save big time (I would have to pm you that info however). If you hire a guy to do the install then you can actually make a apointment with them. Like hey I am having a issue can you stop by at say 8am...... Were as Cable (or sat if you have the freebee install done) it is like ok we will be there btwn 8 and 4 so please make sure you are home...... Hope that helps. If you talk to most guys that do what I do for a living you will find that most of us have Sat. units.