I use a touch screen on my mill running KMotionCNC, and I quite like it, but it really needs a suitable screenset to make the most of it.
My mill does however have a mechanical MPG, so the screen is only really used for selecting programs/options.

As Muzzer mentions, the type of touch screen can cause problems.
Resistive relies on pressure, and should be resistant to any contamination on the screen and can be operated using any kind of blunt item, but they're generally less accurate than other options.
Capacitive (this is probably the most common you'll get now) relies moisture to detect position, so contamination like oily fingers/oil on the screen can cause issues. They'll only work with a bare finger, or a suitable stylus. They won't work with gloves, unless you happen to have ones with conductive thread on the fingers. They are generally the most accurate, which is why they're so popular.
Optical is the other option, and generally falls in between the other two. They're not as affected by contamination, are a bit more accurate than resistive, but they can be affected by external lights.