the tune is by far the best "bang for your buck" mod you'll ever do on your truck... there are disadvantages out there, and as someone said, you just don't hear about them... remember, you're altering factory things, taking out torque management, changing pressures in your tranny lines, altering fuel and spark ratios, etc... so as with any mod that you do across the spectrum, possibilities are out there for things to go wrong, but the failure rate from a tune is pretty much slim to none.. just all depends on how you drive your vehicle and how aggressive you get with the tune.. beat the piss out of your ride, it will break... treat her right, and she will last a good while...
IMO, pros are increased MPG's, slight HP increase, no more lagging throttle response, firmer shift points in the tranny, and just an overall better driving experience in the truck and actually how things should've been from the factory...
cons, there really aren't any... some have had issues with the security relearn and the CASE relearn, some thought the tune was a waste of their money, meaning they didn't feel a difference in shift firmness or something along those lines.. but for the better part of the population on GMTN, TBSSowners, and the OS, the pcmforless tune is the way to go, and none of us have looked back...