What is it exactly, that makes these images appear miniature-like? I can never quite figure that out. I know the lens does it, but what is really happing, I don't know.

A tilt and shift lens can be used to negate the effect of converging lines. When you're at the bottom of a building you tilt your camera upwards to capture all of it and (especially with a wide angle lens) the top appears to narrow inwards.
With a tilt and shift land you reposition the lens so that the camera is level but the image is from the entire building. Appearently this can also be used to make things look like mineatures.

Another effective plus is that a tilt and shift lens can introduce selective focus even though the object is at the same distance as that of the subject. Search it on wiki or google and you'll get plenty result 

With a t&s lens you can alter the plane of the the focus, in such a way that it's no longer parallel to the film/sensor.
This creates a selective focus effect so drastic that it resembles macro photography with life size objects.

Btw, a lot of food-photophraphy is also shot with t&s. Just have a close look at cookbooks, or the 'Allerhande'.

That. Is. Awesome!

Here are some more great examples of Tilt&Shift (some are fake though, with a selective focus effect applied in Photoshop): http://www.smashingmagazine.co../..photography/

very, very cool

You do not need expensive lenses for this effect the same can be done on photographs with photoshopping; one of mine:
http://www.worth1000.com/view.../..=photography.

How to do it:
http://recedinghairline.co.uk/../..s/fakemodel/

Roel, your statement needs a slight nuance ; The selective blur in photoshop is really not the same as the T&S effect. The T&S effect really adheres to the actual depth of field, and in postprocessing you're actually guessing where to put focus.

It's pretty similar, but it's really not the same.