It really seems like its another company jumping on the green bandwagon. Unless you sell "green tools" or sell to communes that try to be 100% green, its just a tacky addon to a website.
I mean, I really do not think anyone cares. I dont think the datacenters are especially "green" especially if they ever have to use catapiller generators, heh.
IMHO
EDIT:
Also think of the backup website you are going to have to buy to display this when your site is down. "Sorry, the sun has not been out much for 3 days, so our solar power generator is not working. The site will be back up when the sun shines. PRAY FOR SUN PLEASE!"