You definately have a point with not raising with jacks preflop, but the thing that makes my decision more simple is that i can usually put people on cards if I raise.

Ex: If I raise preflop, and 2 overs come huge bets, I can safely fold and my only loss is the raise. 4-5BB or so.

If I dont raise, there are many limpers and say the flop comes 568. What would you do. I can see the potential to take down a big pot with someone holding the likes of ace 8, but there is a great potential for straights/draws, flushes/draws and 2pair off the flop. Therefore, even if I have an overpair, I have found that I will lose sometimes for a great deal of money.

It seems raising keeps my variance down while not raising makes me have huge swings in variance.

However, probably the best solution is mixing things up with a bit of both, to keep people guessing. If you only raise with premium pocket pairs or group 1-3 hands then people will put you on those cards.