John Myung seems to use the pads of his fingers quite a lot and doesn't seem to have much trouble. I also use the flats of my fingers when playing more lazy stuff since I can get a lot more strength and down onto the string, but I seem to play a little more like JM in the respect that I play half on the tips and half on the flats when playing more difficult things. Although I'm slowly moving my fretting style more to my fingertips as time goes by.
My problem is I've never had insanely good hands for tiny accurate things (like writing; terrible hand writing :P), so I have a lot of trouble fretting large bass strings with fingertips. Much easier to play on the flats slightly. Fretting guitar strings with fingertips is insanely easy though :/
Couple of videos of JM:
http://video.google.co.uk/videoplay?...9&q=john+myung http://www.youtube.com/watch?v=KsEZT5-cOuY (he plays more with his fingertips in the runs on this one ^^)