I just started a rebuild of an old Raleigh pursuit for a friend...and his bike was in about the worst "grime" condition I have ever seen. I started by pre-spraying the entire frame and wheels with straight SG out of a spray bottle. I let it set for about 2 hours, then came back out and sprayed it all again...30 mins later I attacked it with a steaming bucket of hot water with a healthy shot of SG in it, an old sponge and paintbrushes, and rags. It worked great, as I think the pre-soaking with SG really softened up the nasty stuff on the chain/freewheel, and the hot H20 really cut the rest. I wouldn't have done all that if I hadn't planned to completely strip everything, since this combo would get past seals and into hubs and such. I'm going to post before/afters on this one later, but suffice to say that the rear D had so much congrealed decades-old grease (who the F greases a chain?), grit and matted animal hair (!) that you couldn't tell the pulley weheels had teeth....they looked like big globular black donuts. Yech. After this treatment everything was pretty damn clean. A liberal dose of WD40 a couple times over the next few days got rid of any remaining gunk in the crannies of the derailleurs. I also soaked the chain after this in a bottle with about 2 cups of straight SG, shaking it every few days. After 3 days I took it out, rinsed with very hot h20, and it looks like it just came out of the box.

So, in a nutshell, I'd say use it straight if it's a nasty bike. Makes your shop smell real nice too.