DPI has nothing to do with it really.
You just make it so x movement of the mouse = x movement on screen regardless of the speed you move it at. With acceleration (Enhanced pointer precision on) you will never have a constant movement, it varies all the time so its harder to judge the movement needed.
Its personal preference though..a lot of quake players use some accel but pretty much no counter strike players do. Probably depends a bit on the game type and movements needed. Accel might not be too bad in a game like M&B, it probably won't matter a great deal if you get used to it
