If there is an option, for example ITV1 or ITV1 HD, Nat Geo or NatGeo HD I will always watch the HD version. On a modern 40" LED set the picture is noticeably better even my mother in law will accept that after seeing some of the BBC stuff. The sound is often much better to (if you have an multichannel AV system).
Not a slave, as I have not moved any furniture or hardware, but a fan.
Given a choice would you watch a film on VHS, DVD or Blu Ray??
Footnote my mother in law has subsequently gone with Sky HD service........