Actually, limping with non-paired hands is about the worst thing that can you do
Ok, lets sort this out.
Typically in a full ring game people limp for three reasons.
1. They want a cheap flop with good implied odds.
2. They are trapping to limp reraise with a big hand.
3. They suck and are playing trash or are passive and dont want to raise (these players suck btw)

Comon knowlege suggests that if you hit a set with a pocket pair, a hand you can limp in ep that has good implied odds then you are almost assured of having the best hand whether the pot is raised or not.
This is common knowledge and an easy way to beat the game when its full of bad players.

HOWEVER.
The game dynamic is begining to change.
Players, especially full ring players now recognise the typical flopped set line, particularly in a raised preflop pot when a player limp/called a raise. Thus players are now raising with PP's in the hope of building a big pot when they flop their set which also allows them to use their fold equity on the flop becasue of the asumptions made by other players when a player raises preflop.
Thus, players may raise AQ and make top pair but they may also raise 77 and make top set.
Thus ep play is no longer just about not being dominated, it is about using implied odds to theor maximum effect.

As a result, as theory and Practice now points out, and as the more studious players have begun to realise, limping in ep with drawing hands is now much more +ev because raising the flop with a draw will put tptk hands off playing big pots because the think they may be against a set. The flush draw/oesd line and set line can be played in exactly the same way with exactly the same amount of fold equity.
Therefore, it is NOT NECESSAIRLY (sp) bad to limp in ep with QTs because of the changing shape of the full ring game.
However
1. You need to be playing with players who recognise this.
2. You need to be playing at stakes where players are actually able to fold tptk.
3. It only works in passive games where not a lot of raising goes on preflop but a lot of players go to the flop. (and yes, if you apply good table selection then everyone of us should be sat at these tables anyway, not rockfests)

but if give the choice...wouldnt you rather be the one raising and making the other guy fold top pair?cant you play any two suited or connectedcards and hope to murder a flop?
So realise that the game can advance beyond the simple strength of your cards. Eventually, lines become evident that will fold certain hands or force players into big decisions. Limping in ep with drawing hands is one of these possible developments because of the effectiveness of set farming over the last 12months or so as poker has grown along with bonus whoring.