Hi,
We have thermofoil cabinets as well. Basically the door's core is MDF material and is finished with a plastic film that is heat shruck to fit the door' surface. Now, because we are dealing with MDF, screw and nail holes MUST ALWAYS be predrilled. That's about it really. You didn't say what hinges you were using but predrilling is required. Use a drill bit that is sized for the shank of the screw or a little bit smaller. What's the shank? The shank of the screw is the long part that the threads are wrapped around.
Ever notice when trying to drive in a screw and it either won't go in, or it busts up the wood material? That's all because the shank has no room to make its way into the wood. If the screw has an agressive thread you probably will get the screw in but you will damage (loosen) the material around the shank. This is the area that the threads are trying to bite into. If the surrounding area is loosened the screw's holding power will eventually fail.
So predrill, it will lengthen the time of your install BUT your doors will hang in place, true and square for a long time...until the kids come by and decide to hang off of them. :-)
Woodwork Safely,
Jim Barry
www.WoodchuckCanuck.com