I used to use Simple Green for cleaning paint off pre-owned miniatures. That's what Hubs introduced me to when I got into the hobby and it worked well enough. I have a few problems with Simple Green, though, the most glaring of which is the toxic fumes it gives off. Ten minutes of scrubbing a mini off and I felt light headed, bordering on passing out. No good.
When I faced cleaning 120+ Dwarf models with that, I felt some dread. I mentioned my dilemma to Richard and he suggested I try Dawn Power Dissolver, which he liked. I used to it clean my Dwarfs with great success. Right off the bat, I was pleased it didn't smell as though it's killing my brains cells. It's pleasantly soapy.
It also didn't require nearly as much soaking time or scrubbing as the Simple Green. Simple Green needed to sit a few nights. I left the Dwarfs overnight, but I've learned since then that it'll do a great job in less time than that. Unless there is paint caked on the mini, you could let it sit just for a few hours. It cuts down a lot on the whole process.
I discovered that in addition to removing the paint, it can also weaken the glue bonds. So, if you have a pile of poorly assembled Tau you scored on eBay (like some people I know) then after a little soak in this stuff, their arms, guns, etc. will pull right off without damaging them, so you can reposition the figures. It doesn't work on all glues, but without knowing what the figures were assembled with in the first place, I can't say for sure which ones do and don't. It's a little hit and miss. It didn't seem to bother the glue on the Wolfen, but I also wasn't trying to pull them apart.
An important thing to keep in mind is that you cannot use water to stretch the stuff out. It warns you not to add water right on the bottle, presumably because it doesn't work after that. Good news is, it's less than $3 for a bottle so if you need a lot, it's not going to break the bank. If you want some, you'll find it in the same aisle as the dishsoap in your local store. I've only seen it at Walmart, but I haven't been looking for it too hard in other places.
Coincidentally, it also works fabulously for cleaning old gunk off baking sheets or pots and scrubbing off your stove top. It's nice to see that it works well for its intended purpose, too. For the dishes, I generally don't have to do any scrubbing, unlike the miniatures. My minis and my dishes have never been cleaner!
It is with great sadness that I must update this post to say that Dawn Power Dissolver has been discontinued. It was a wonderful product and I will miss it (so will my dishes). I have no idea what I'll use to clean minis with yet, but when I find it, you can bet I'll write a post about it.