WD-40 was not invented as a lubricant, or even as a penetrant. It was designed to simply displace water to prevent rusting. The inventor had tried 39 different chemical concoctions before he found one that worked. In the lab he called his different attempts WD (for water displacement) 1, 2, 3, 4... When the 40th one finally worked, the lab name stuck and it was marketed as WD-40.
Just think, if he had been a really bad scientist, we could all be running to Wal-Mart to pick up a can of WD-147. Just doesn't have that ring to it.
Of course, since WD-40 does it's job (displacing water) through the use of low viscosity petrollium distallates, it naturally has some lubricating and penetrating qualities.
But if lubrication is what you want, then it's better to stick with something that was designed to do just that.
However, if I only have enough space in the toolbox, car, or boat for just one utility player, WD-40 is on my starting lineup. I have used it for preventing rust (imagine that), lubricating, petetrating, de-greaser/de-gunker, anti-seize, cleaning sap off my paint and bumper stickers off glass/metal, fire-starter, gun cleaner, case lube when resizing brass, ant-killer, and even as an attracting scent on fishing lures. And if someone puts a little bit on your potato chips when you're not looking, it works pretty good as a laxative too (don't ask).
Basically, if I have a problem and I can't figure it out, I don't have the right tools available or I'm just simply frustrated, I shoot the problem with WD-40. Ususlly works.
I think the guy who invented the stuff should be awarded the Nobel Prize.
Semper Fi,
Culprit