We found that the leak under our sink was caused from a poor seal under the faucet plate. I loosened the faucet assembly and put a bead of silicone under the edges, tightened it back up, and haven't seen any more water down there.
I am on the lookout for leaks all the time, anything that twists and moves is gonna loosen fittings. The only other plumbing problem we had was the shower drain pipe was cross-threaded from the factory. I was opening the valve to the water heater and noticed where there had been water leaking. We had tried the shower for a few seconds just to see if the pressure was good from the showerhead, and that was enough to dampen things pretty good down there.
It will keep a person vigilant (paranoid?) about checking under plumbing fixtures!