Elanto: I'm a little curious about the stats you posted below.

Seen JJ: 25 times
Hit Set: 4 times
Hands Won After htting set: 1 (lost to 2 flushes and a str8)
Hands folded after the flop: 8 times (2 overcards have hit the board in each and every1 of this 8 times)
Hands lost wihtout hitting set: 10 (beaten by 2 pair, higher pair, etc)
Hands won with JJ without hitting a set: 3!!!!!!

Particularly, the 4 times you hit the set of Jacks, did you attempt to slow play them to a board with 2 or three straight or flush cards? I acknowledge that there is a temptation to slow play a set to build the pot, however, to a scary board this can be fatal. I'm not sure if you're talking about NL or limit here. I play mostly NL. When I flop a set and the board is scary, I push hard so that anyone on a draw has to pay dearly to try to make it.

By the way - I don't much like pocket Jacks either