Hey Jef! Boy - our old pal, Nigel, really likes to take this stuff down to the molecular level, doesn't he?
We love Nigel and reading his posts but, I'm gonna try to answer your question with 20+ years of bike wrenching under my belt and balance it between what I have seen people do with WD-40 and what I have seen published in certain magazines/books over the years, along with my own thoughts.
Nigel - please keep in mind that many folks outside of our BT membership may read this and that I am in no way intending to discredit you. Cool?
Rule #1 : JUST SAY NO to WD-40. It's a Penetrant. Not a Lubricant. The same goes for Liquid Wrench, Nuts-Off, etc. If you need these products, you really need a new chain.
For the average cyclist that likes to perform thier own maintenance, Simple Green is a nice-smelling and environmentally-friendly cleaner that can be easily used straight and then progressively diluted in those chain cleaner tools made by Park, Pedros, Finish Line and others. BUT. When you go to dump the contents of the tool... is it still environmentally-friendly junk? Probably not. If I'm trying to salvage a usable chain on a customers (old) bike that looks like it's coated with tar, cat hair and belly-button fuzz, I'm gonna get nasty and use kerosene or diesel fuel. Sometimes I have even had to resort to carb cleaner or other harsh chemicals. That's another story, though.
If I may - I need to diverge to a tangent subject here. When these chain-scrubber tools first came on the market back in the 1990's, I thought they were the next biggest thing since sliced bread. I, personally, no longer use them. Why? Re-read what Nigel posted and think about it.
The lube (grease) that is In/On a new chain from the factory simply can not be beat, but, unfortunately it doesn't last forever.
When I sell a new bike or have a customer pick up a repair that needed a new chain or drivetrain, I inquire about thier riding habits and conditions. Chain lubes have become very specific to these parameters, these days.
The main thing is - Once the factory lube is gone, it's up to You. Keep it as clean as possible. Do Not over-lube. That attracts grit. Grit + Lube = black carpet. You only need lube down inside the rollers and bushings. The rest will get residual lube as it creeps out of the link.
Wheelies don't pop themselves. (from a QBP fortune cookie)