[Andy B]

The guy who starts with a pair has something like a 16% chance to hit his set if he stays in until the river. One-pair hands can't handle a lot of pressure and are frequently folded before the end. Meanwhile, if you're rolled, you've got a 40% chance to improve yourself. The guy with one pair isn't that great of a threat. I'm a lot more worried about straight and flush draws.

As for taking your Jacks against open Queens, let's discuss a couple of possible scenarios. Let's say that the Queen raised third, and you called with Jacks because there was a Queen out and you like to gamble. The other guy now hits open Queens. If, as is typical of low-limit stud players, the other guy will only raise third street with big pairs, his possible distribution of hands might look something like this:

AA 6 ways
KK 6 ways
Qx 41 ways
JJ 1 way
TT 6 ways

So it's overwhelmingly likely that he has you crushed. You can't call with JJ in this spot, and it essentially doesn't matter how big the pot is.

Now say that you were the raiser with your Jacks and he called. He probably has something, and maybe it ain't much, but enough for him to call with. There's at least some chance he started with split Queens, and maybe he didn't raise because he didn't like the dead cards or maybe he's scared of his own shadow. Maybe he started with a pair in the hole, in which case you're drawing to two outs. If you have an over-card kicker, it's five outs, but he can still outdraw you. Here, you're not in good shape, and it is very unlikely that the pot will be big enough for you to stay with him. If the pot is big, what the hell are you doing in a big pot with a pair of Jacks in the first place?

Even if the guy "only" started with a three-flush, you're behind, and on balance, the pot isn't going to be big enough to justify look him up. If you never called when you were beaten on board, you wouldn't be far wrong. I make an exception if I have a strong draw and the other guy has an open pair but doesn't seem to be that much of a threat.