Arduino controlled PWM PC Fan
One thing to note is that 


if (pwmVal != 255) {
    pwmVal += 10;
    ...


is not going to stop at 255, since pwmVal will be 250, then 260, e.t.c. One way to fix this would be write


if(pwmVal &#60 255)
{
   pwmVal += 10;
}
else
{
   pwmVal = 255;
}


By the way your code is written, if DEBUG is set to 0, nothing will happen (pwmVal will be set to 0). If DEBUG is set to 1, the fan speed will increase at a rate set by "wait" (which isn't defined in this code), until it gets to it's maximum. The value will also be printed to the serial port.