HD channels will kick off big time when the analouge channels are finally shut down as the amount of bandwidth available will increase along with the strength of current freeview stations.
There are apparently moves to start broadcasting HD on freeview from this summer and plans for a PS3 gizmoto let you record it onto your console.
As for HD being rare I think anyone buying a TV today would be opting for at least a 720p HDTV if not a 1080p as they are dropping in price dramatically. I bought a 37" 1080p for £499 with 5 years warranty and its excellent.
Blu-ray movies look stunning and as soon as motorsport makes its way to HD im going to be dropping my jaw - golf and footy already broadcast HD too btw
