well - we have it because DH has sky sports and likes to watch the cricket in HD, but it is nice for some BBC Attenborough shows and LOST in HD on sky.
If we didn't have the sport though I wouldn't think it was worth it currently for the small amount of true HD stuff that's on. But that will change, there is more and more on as time passes.
Some of the boxes are laggy though, we have (i think) an Amstrad HD box and it is very slow in terms of remote control response and it is incredibly annoying. Not all of the boxes do it though.