Leading edge slots such as shown in Mikes post should have no significant effect on the cg or performance in normal flight attitudes. There will be a small (but probably not noticable) drag increase in normal flight attitudes. The slot transfers energy to the upper boundry layer which delays the stall to a higher angle of attack allowing the wing to produce more lift before stalling. It's a nice addition to be true to scale, but won't really effect the flight characteristics much.