I've just hung up a full (9kg) load of washing. It took me half an hour.
I may be unreasonably slow (but kids/ babies= a lot of very small items in a load) and I totally agree with the environmental arguments - but why, when people say 'oh, you can save loads of money by hanging your washing up' do they never talk about how long it takes?
(I don't think it costs as much as £2 to run a full load through our tumble dryer. Even if it did, that's £2 to buy back half an hour. My hourly rate is well above £4...)