Right, before everyone jumps on the bandwagon screaming how great these miniature edits look, I'd like to point out that in my opinion there is still a lot to improve on the miniature pictures. The topic we are talking about is generally known as
Tilt Shift Photography which can be used for making miniature look alike picture.
I googled for a quick tutorial, and
this one seems ok. The pictures that were posted here before I think suffer from a very sharp line between the heavily blurred area and the non blurred part. I think there should be a slight and smoother transition, as well as a tiny bit less blur.
You may want to look
here, and see a lot of great examples of real life pictures. You can see that the blur does not have to be always so uber heavy, as well as it doesn't always have to be on top/bottom at same time.
Anyway, my 0.02$, I think it's worth checking the links, and try and improve those edits a bit.