So I bought one of these kits, and it's really hard to use. Basically you're trying to squeegie a piece of glass to get the little particles off of it that are literally microscopic. So it goes: take the lens off; squeegie out the camera guts; put the lens back on; take a picture; download that to the computer; note that you've made the specs worse; repeat until you reach something that seems like a local maximum. BLEH! Maybe it'd be easier if I had a really huge magnifying glass.
This process has also made me realize that there's a whole different set of spots on the path that goes lens→mirror→viewfinder than the path that goes lens→sensor.
Getting someone else to do it is a hassle too, as the local shops seem to just send it off to the manufacturer for cleaning, with a 2-3 week turnaround time.
(Did you know that the HTML entity for → is →? Who knew that arrows were so piratey.)