To be honest there's not an awful lot of content, SKY ONE HD is misleading as loads of their content is SD. It's getting better, CH4 soonish and BBC HD so for £10 a month i'm happy. Also got my box for £149 five months ago, would not have paid £299 for it though.
I mainly watch/record HD movies and find myself re-watching some of the ones I've seen. Watched the spurs game today, I think sport looks great, really shows HD off. Strictly looks great too, you do tend to 'pine' for HD when not watching a program in it.
Some other highlights are HEROES, ICE TRUCKERS, JOOLS HOLLAND, TORCHWOOD
The big question is, what size is your TV. If it's smaller than 40" it's probably not worth investing in HD unless you sit 3 feet from it!!
My g/f is very happy with the purchase, I've got a Pioneer 428xd and Sky HD looks awesome.
R