Samer1970 :
no it will not fit in most ATX cases ... it is longer ! atx is 245 long while EATX is 310-330
E-ATX is UP TO 330mm, but that doesn't mean E-ATX boards are always that wide ( deep, for the server crew ). Plenty of boards marketed E-ATX are just barely over the ATX spec at about 10.5" / 270mm or so. These can often fit in a normal ATX case, with the forward edge just creeping into the cabling grommet and punch outs. I have one such setup right now. And I'm willing to give MM the benefit of the doubt that he simply missed typing an "E" in that last post.
His original point about the stand-offs and holes not being the same between E-ATX and SSI EEB is the more salient point. Even if you could fit the board in an ATX or E-ATX case, you wouldn't be able to mount it without significant modification.