Speaker Wire Length Question

[spark001]

My receiver is located in the TV stand below the plasma. Therefore, the speaker wire run to the front speakers is much shorter than the run to the rear speakers, which are mounted on the wall near the ceiling. The rear speaker wire runs go below the floor into the basement ceiling, then across and up into the wall to the speakers (which are about 12 ft back from the receiver/tv. Running length would be much greater). I'm curious as to how picky you guys are to having ALL your speaker cable lengths the same. Is there a recommeded limit to the difference between the length of the front channels compared to the rear channels? Does it really make a diffence? Thanks!