Broadcast HD is wildly overrated. All this nonsense from people who describe it as "looking out of the window" is just that... nonsense. Unless they have a really crappy, pixelated view from their window, that is.
Now, it's certainly better than most SD broadcasts, but just not to the extent that some people claim, because they just forked out £1500 on a new HD set. There's even less of a difference between SD and HD on "HD ready" sets, which only do 720p. You also need to get close to 50" to really notice much of a difference from a normal viewing distance.
Professionally mastered BluRay movies really do make a difference, though, if you have a 1080p capable set.