It is absolutely worth it. Without 1080, bluray is pointless. There still isnt much 1080, if any, content broadcast publically but if you're making the investment, go 1080 and 100hz. Should last a good while.
A good bluray player, i.e PS3, upscales normal DVD's and is quite noticeable.
1080 is razor sharp, 720 not so much. IMO 720 was just a marketing ploy.
Edit: Virgin does do 1080, Sky does not as far as I know due to bandwidth issues. Also, a PS3 is a worthwhile investment here, its one of the best bluray players around (of any price level) and you can stream HD video directly from a PC if you have windows 7 and a decent network setup. I did it instead of building a media center. Worked out loads cheaper.