I have UD running on my machines. My work PC is on 24/7, but my home PC is a real beast so I only turn it on when I actually use it, otherwise it would add another 8-10$ (well, the equivalent in yen) to our monthly electricity bill. I know this from observation, I used to run the PC all the time, then one time I decided to start shutting it down when I was done with it, and the change was clearly noticable on the monthly bill.
BTW, compared to cancer research Seti is a total waste of resources, IMHO.