How far will HDMI go? I suspect it's only a short distance spec
measured in metres...

15 metres

To answer my own question, the recommended approach for long runs is a
converter to use a pair of cat5e's:

http://en.wikipedia.org/wiki/Hdmi#Extender


It might be worth adding that putting in at least one quality coax
cable to every room is a good idea due to the disruption that putting
cables in makes.

I'm told a pair of coax's to wherever a dish might be installed is
also a good idea.


What about cabling in home cinema?

After posting, I thought of integrated/multiroom entertainment systems
as well.