As I understand it, Squick refers to a reaction from the audience (or a character in the work).
Nausea Fuel is what provokes that reaction in the first place.
This is a bit of a zombie, but I see the question was not answered. Squick is locked because it's mostly about sexually disturbing crap, and people would not stop adding examples. It's actually missing an important part: the word actually came from the sound effect someone made to someone literally fucking a skull. Anything that provoked a similar reaction later became called squicky. It's a combination of sex with icky things.
Nausea Fuel was always a lot more general. It didn't necessarily have to do with sex at all. For example, seeing someone eat poop might be Nausea Fuel, but it's not {{squick}] unless it's supposed to be sexual (and I'm sure you can think of an example of the latter. Here's the Brain Bleach for you.) I'd guess NF hasn't been locked because it hasn't been abused to the point where people were seriously grossed out by it. The lack of focus on sex makes it a little less icky, and thus also makes it not nearly as good for trolls.
Everyone Has An Important Job To DoBigT, stop necroing threads, please?
"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"Actually, I think a stickied version of this thread wouldn't be a bad thing. If nothing else, we could get more attention for the Canonical List of Subtle Trope Distinctions page (or whatever the proper page is).
edited 6th Mar '11 1:13:23 PM by Deboss
Fight smart, not fair.

From what I can tell the latter is identical to the former, except with examples.