WD-40 is the only thing that touches my chain.
Before the naysayers go bananas, please note that WD-40 does not
contain silicone, kerosene (the most popular misconception, "It will eat your O-rings!!"
-NOT!), water, wax, graphite, or CFCs.
Folks who say you can't use WD for chain cleaning -AND-
lube are, frankly, full of bullsheet.
I know several people who have used WD exclusively for this purpose. An FZ1 rider I'm aquainted with has a whopping 19,000 miles on his original chain using WD once a week. No sign of substantial wear yet.
He rides plenty hard too, lives in the twisties near Palo Alto, CA.
In days gone by I used WD for cleaning my chain, then I'd blow it off with compressed air, then I'd apply Maxima Chain Wax for lube and rust protection. Well, I didn't like all the crud the wax would attract to the chain over the course of the next few hundred miles before I repeated the process all over again.
So I decided to nix the second step, namely, the wax that I would work so d**n hard at getting off with WD during maintenance time.
I'll never pay for "chain lube" at a bike shop ever again.
As a final footnote, I'm familiar with a guy who wrote WD regarding this issue (and actually got a response back - I'm sure the company gets ALOT of pestering e-mail inquiries).
"WD-40 is a multi-purpose light lubricating oil. The WD-40 will definitely displace and remove the water or moisture from the chain. The 'WD' stands for water displacement. It will also act as a rust preventative on any of the metal surfaces. WD-40 will not 'dry out' the rubber o-rings. We have found no visible effects on surfaces of rubber, and o-rings. Certain types of rubber will swell under prolonged immersion [emphasis mine] in WD-40 (this refers to long soaking, and not just a spray)."