Ive never had much luck with the Arctic Butterfly. In fact the first time i used mine it seemed to get oil or grease on the sensor and i had to by a wet system to get rid of it.
I think the a few of the fibres might have touched the side as it was going in.
I just wanted to point out to felix that while something can go wrong, although not very likely, your not actually cleaning the sensor, its a Anti Aliasing filter (in most digital cameras, not all) that your cleaning so if the worst does happen its not going to cost the earth to get it fixed.
Definitely worth learning how to do it yoursefl IME.