The WD in WD-40 stands for "Water Displacement" and when mixed with water it becomes kind of soapy. When I worked with Ryan Linville at Bike Works a few years ago he taught me a neat trick he'd learned at a shop in New York. Ryan mixed WD-40 with water and put it in a plastic trigger spray bottle. He called the stuff "Bling Juice" and depending on how strong you want to make it you can play with the ratio of WD-40 to water. Two parts WD-40 to one part water works pretty well, but a 50/50 mix makes the supply of WD-40 last longer. You shake it up and you know you've got the ratio right when the result is kind of foamy & white.
Bling Juice is really good at cutting through road tar, grease and drive-train gunk. It does leave behind a film, so don't get it on braking surfaces or brake pads. It will clean away crusty & dirty old lube, so be sure to re-lube parts that need lubing with a real lube after you've done your cleaning.
So that's my tip for the day. WD-40 mixed with water. It's lousy as a lube, but it's wonderful as a cleaner.
Keep 'em rolling,
Kent "Mountain Turtle" Peterson
Issaquah WA USA