"Compared to a response rate for an advertising campaign, 0.25% is certainly poor (from what I know about average rates)... but this isn't really the same thing, is it?
IMHO two better comparisons might be:
How many people go onto the Channel 4 chat-room after watching a given programme?
How many people write into programmes to get information packs by post?
I don't know what the rates for these are, but they seem like a better comparisons: they're calls to action, undertaken at the expense of the viewer, and involve stepping out of the medium currently being accessed (TV) and using another (internet, the written word)..."