Most DTV and Cable boxes currently have very rudimentary apps to show weather, sports, etc ... but they are slow and ugly looking.
Google/Android opens it up to support tens thousands of apps, very good web browser, flash, etc. Through it's open source nature, it will encourage developers to come up with innovative new ideas. What they have done in the phone market in the past year has been amazing, and I suspect this will be just as impressive.
Dish Network has already jumped on the bandwagon for Google TV/Android.
DTV just rolled out the excellent HR24 receiver, which has 3 tuners and works with remote H24 units. They're also working on a DirecTivo box, which keeps getting delayed. I suspect it'll be a while before DTV commits. I prefer DTV to Dish, and hope that they offer a Google alternative as well!
The cable company boxes have software that is absolutely terrible, IMO. Bare bones functionality.
It's probably good to leave the hardware vendors to make hardware, and someone else do handle the software.
In any case, it should be interesting to see how innovative this gets. Google tends to have a lot of surprises up their sleeves.
Mike