Are Samsung NX lenses the same as Sony NEX lenses?
No. The Samsung NX lens mount and the Sony NEX lens mount are different. Someone really ought to shame them for their relentless mimicry of others. While they're good at it, the intentionally introduce confusion.
Can I use non I-function NX lenses on current cameras?
Sure. But you won't have an I-function button on the lens, obviously, and thus can't invoke functions from the lens.
What's the actual focal length of the NX lenses?
The focal length is always stated correctly on the lens (and in my pages). Because the Samsung cameras use APS sensors, however, the angle of view that these lenses cover is 1.5x what you would expect if you were using a 35mm film (or full frame digital) camera. For example, the 16mm Samsung is equivalent to a 24mm lens on a 35mm film camera. See my article on angle of view.
What does the term pancake mean?
The 16mm, 20mm, and 30mm lenses are often referred to as "pancake lenses" because they are incredibly thin; they don't stick out far from the camera. Any lens that has very little length to it is invariably called a pancake lens by enthusiasts. Some people refer to the 20-50mm lens that way, too, but while it's small for a zoom lens, it really isn't quite what most people would call pancake.
Who makes these lenses? Are they any good?
Samsung designs and makes the lenses, though I suspect that they get some design help and glass from other Korean makers, such as Samyang. And most of the Samsung lenses I've tried so far are quite good designs optically. I wouldn't avoid the Samsung lenses just because they're made in Korea.