I needed to order some things from ThinkGeek anyway though, so I tossed a few interesting things in there for the ride, which is really why I got this. Here's a photo-review beneath the cut.
You can see how it slowwwwly deforms as you bloop it out of the little 'airtight' container, and it's high viscosity. It smells very strongly of Pixie Stix or Energy drinks, and some kind of plasticizer I think...don't take a big whiff when you open the thing up, like I did. whewwww yikes.
So this is what my keyboard looked like before: fucking gross, just like yours. Except mine is sitting right next to my wet bench, and I do a lot of in vivo things around there.. Shouldn't be a cesspool of filth, but it was.
You just smash it onto they keys directly, and let it slowly work its way down into the recesses. It's cold and a bit rubbery, so you need to be slow and steady in working it in. It feels like it might dissociate and stay down there, but it won't. 
I personally am not a fan of the feeling of squishy and squashy and goopy things like some people I know... but it's an interesting texture nonetheless.
It keeps a shape well enough when you pick up your hand, for a few seconds at least.
Now peeeeeeeeeeel it back up, slowly slowly...
And you can see (maybe not so well on this photo) all the gross that that it collected on and between and beneath the keys on the keyboard, displaying your filthiness for all to see.
But look at the keyboard now! Wow, nice job. You'll need to go back on the sides on some areas to catch everything, and it won't go all the way down to the bottom of some deeply-recessed keyboards, but the most obvious stuff on the visible sides (the 'inter-dental' areas if they were teeth) are gone, baby.
Let's try again on another area. Here's before -- fillllthy.
Smash and squish and smidge it down on top of the keys..
Admire the big snotball you put there and wonder how it's going to do anything but make you look like you don't cover your mouth when you sneeze..
Peeeeelll it back up..
And look how clean your keyboard is.I'm a fan of this stuff already. It says you can re-use it for a number of keyboards until it gets saturated with gross. I'm going to put that to the test for sure. I already tried it on my mouse, and it did a decent job there as well.
If your keyboard is filthy and don't want to toss it, give this a try.
