Airspirit's right: you'll loose about a third of the refresh rate with a flat panel.
The refresh rate is important if you're going to be spending a long time on that PC (i.e. a few hours at a time), because a lower refresh rate will strain your eyes much faster.
It's also important for action games, because I'm sure that you don't care to see shadows of things floating over the screen, although that shouldn't be much of an issue, nowadays.
Of course I'm assuming that you do take the time to set the refresh rate to its maximum value; a lot of people leave it to the default 60 Hz...
