From a completely unscientific method using memory and simply lifting the keyboard, the 9008 is pretty close to the Filco in weight. Maybe if you had them sitting side by side, you might be able to tell, but according to some folks who would be in the know, the 9008 is OEMed through Costar who makes the Filco 'boards, so the quality and certain design elements are fairly similar. If the 9008 does, in fact, have an aluminum plate, then it will probably weight a little less, but not so that you would notice by feel. Between the weight and the stout rubber feet, it won't be moving around your desk at all. You would be doing yourself a favor in getting this 'board. I really enjoy my 9008 and have a G2 with browns coming tomorrow or Wednesday.
I know I might be evangelizing a bit, but IMO, the 9008 is the best full-size Cherry 'board on the market. The new Leopolds would be the only thing on the market soon that might be close or better. It's definitely better than Filco, IMO.