Like XTR said it is all dependent on how lightly someone will stack off when we hit our set.

Against someone that only plays AA/KK PF we can pretty much use our effective odds of hitting a set, something like 7:1.

However, against a player who play 25% of his hands PF in this manner we must consider a few factors:

A. Our position relative to the PF aggressor
B. His position and how it relates to his hand range
C. How likely he stacks off
D. How deep the stacks are

To answer you original question, you should generally not be calling off more than 10% of your stack PF with a low PP against a tight opener. Against a loose opener it might be something more like 7%.

If a loose aggressive opens in MP to 4bbs and you have 44 by all means call. Typically we should not be calling 3bets PF with PPs unless the 3better is an extremely tight player and would only do so with AA/KK. A typical 3bet might be 12% of your stack, which is borderline for calling a 7 to 1 shot.