We're thinking of going down this route as it's a heck of a saving for us given the huge lecky bills we have. Need to get in fairly soon though, as the govt are proposing changes to the feed-in tariff starting next April.
If you don't have the up-front dosh there are schemes to allow the company to bear the cost of the install and to effectively "rent your roof". You'll still save dosh
Trouble is, I've seen some installations that are not the best aesthetically......