Depends on the TV. I have a Samsung and there is an app in the market that works like the full remote. It operates through WiFi. Doesn't do anything for the cable box, so it's real world use is limited, since it won't change the channels.
I discovered something new tonight. Using the Samsung TV Remote app on my Xoom, I am able to turn on and operate my Sony BluRay player through Anynet+ . Doesn't seem like much, but it's pretty convenient, and kinda cool.