I have a terrible problem. I have a tendency to repaint my models. No, rather, I have a NEED to change my color schemes. I'm not sure if it's because I get bored with my current schemes, if I think I can paint them better than they were before, or I'm just too cheap to buy new models to paint up in new schemes.
To be honest, it's probably a combination of the three.
What I have been using to great effect is Super Clean! I get it at Wal-Mart in the automotive section for about 7 bucks. The jug holds about 2 gallons worth of cleaner which is more than enough to strip 50+ models at once. It's reusable as well, so those 2 gallons can strip whole armies if you are willing to do them in sections.
The degreaser doesn't have a harsh chemical smell. I tend to get headaches when using strong chemicals, but I've yet to get one messing with this stuff. even after a couple hours straight.
It is also biodegradable. No need to dispose of it in any special manner. Straight down the sink it can go. (The stripped paint on the other hand...)
It takes roughly 24hours to take off GW style paints, up to 48hours if you've applied heavy varnish afterwards. All it takes is a old toothbrush and some gentle handling to clean the paint off. No scrubbing is needed. In fact, I'd discourage it to avoid breaking bits off your models.
Easily the best part is that soaking your metal or plastic models in there for extended periods of time will not damage them in any way. I accidentally left 2 squads of genestealers in a tub right before I moved to my new apartments and promptly lost them. Three months later I found them in a bits box still swimming in the purple waters, unharmed in any way. (I have no idea if resin can be stripped using this stuff as I've yet to try.)
A couple final things to mention. This stuff will give you chemical burns if you handle it for 15min or more. They hurt like hell and let's not even mention what happens if you happen to have a paper cut already. Make sure to buy some latex gloves before sticking your hands in, you'll thank me.
Super glue bonds will weaken considerably, so don't expect your conversions to stay in place. In fact, you might be better off cleaning up any super glue residue as you clean off the paint. Don't worry, it comes off clean. Super clean!
Finally, make sure to rinse your now clean models in warm, soapy water. If you leave any residue on your model and try to paint over it, the whole layer of paint will rub right off. Frustrating doesn't even come close to the level of emotion you'll feel.