Hmmm, am I the only one who uses WD40 for routine chain cleaning? I've always done this, since I was a teen. I spray WD40 liberally on the chain and rear cassette while turning, brushing, and using a rag (and rag strips) to get into nooks and crannies until all the gunk is gone. Once most of the solvent has been mopped off and evaporated then I reapply lube.
If I were doing a full chain clean (taken off the bike, degreased, rinsed with water, and dried fully before re-lubing) I'd feel more comfortable using a degreaser and water. But I always worry about degreaser residues as well as water left behind causing corrosion and interfering with the chain lube. I figure using a petroleum solvent like WD40 is safer, the worst it will do is dilute your lube a little bit.
Question about the chain master link stuff - I want to get one of these but I seem to recall reading (on Sheldon Brown's site, maybe?) that you can't use a masterlink with Shimano chains. I heard that you have to break the chain and install a new connecting pin every time. Is this true?