It's a Compel from the GM on your High Concept whenever your Catch comes up. This is explicitly stated somewhere, I think, and strongly implied lots of other places.
I'm torn on this issue.
The Catch has already been paid for, after all, and thus it seems like 'double-dipping', to me, to be paid in compels for the failure of toughness powers where the Catch is applied.
Running water shorting out a wizard's spellcasting? Compel.
Fire burning a BCV? Paid in advance.
I think the thing we're getting mixed up with is that a Catch has out of combat complications. It specifically states under the Catch:
YS pg. 185
Even the mere presence of the
thing that satisfies your Catch will cause
you discomfort (and may be grounds for
a compel or something similar).
So I see these compels as happening in social situations, for instance. If your catch is silk, but you have to seduce the girl...unfortunately she's wearing a silk bra. That kind of thing.
I'm not really sure you'd get a FP every time you encounter something in combat that has your catch. So I'm kind of with the "paid in advance" thing.
If your catch is holy, do you get a FP for pissing off a Knight of the Cross? probably. But that FP was for pissing him off, not for the fact that he's going to hit you with his holy sword.