Bob_the_godly_dude said: That rat looks cool, you mean you can plug one input in and get two out?
As for a use for two in/two out, it would be cool if you had a stereo guitar or stereo effect before it.
Also, there's the Peavey Dirty Dog:

Never used one but they look cool.
I was gonna track one down when I was on the hunt for a nice 2-in-1 pedal, but the reviews of it are kinda iffy. Still wanna try one though.
Definately wanna try a Deucetone at some point too, I love my RAT2 longtime, I like the idea of more RATTY goodness from one pedal..
Re: the Jekyll & Hyde, I had one for a while but didn't quite get on with it. My review is 2nd down here if you fancy an in depth..
The lead and left rhythm guitars on the Weevil Knievel stuff (see sig) were done with the J&K if you're interested in checking it out.