This whole push by the TV industry to buy HD ready TVs has been one big con and is just their attempt to sell lots of TVs.
Sky offer HD but there are few channels and it cost a LOT of money to buy the HD box (�299 I think) plus an EXTRA �10 a month over your normal subscription.
Currently not worth doing.
It will be ages before we get HD on Freeview, and so by then the HD TVs may be better technology and cheaper.
The best HD TV is 1080 lines progressive scan (called 1080p) and most HD TVs sold today are only 768 lines, so when proper HD TV comes out showing 1080P most people who have bought TVs already will not be able to get "proper" 1080p HD anyway.
If you buy a new DVD player that plays BluRay or HD DVD disks then I believe these disks are available in 1080P format, so you can get HD on your TV using a HD DVD or Blu Ray player.
More on 1080p here
http://en.wikipedia.org/wiki/1080p