A fun and easy test for your keyboard's N-Key rollover ability is to hold down both shift keys and try to type in the following:
the quick brown fox jumps right over the lazy dog
Right or not it still gets the point across.
the quick brown fox jumps over the lazy dog - razer tarantula... well at least it's good for something.
XArmor U9BL-S plugged in via USB
Both shifts and caps lock: the quick brown fox jumps right over the lazy dog
two shifts + caps lock on model m = no output
apple aluminum two shifts + caps lock
THE QUICK BROWN FOX JUMPS RIGHT OVER THE LAZY DOG
2009 Macbook Pro
Macbook Pro 13 ", 15" (i5 version)
Logitech K340 Wireless
Microsoft Digital Media Pro
PC Concepts SK-6000