A CRT based front projector, maybe. For a digital projector, no; not unless you've got multi-Gauss magnets in the speakers, in which case you're also going to have troubles with credit cards in the neighborhood.
what leo says. Unless you have your rear speakers right next to a CRT projector, which I can't possibly imagine, it's not a problem at all. And even with a CRT projector, it's not much of a problem like it would be with a direct-view CRT display. There were/are CRT projectors with built-in speakers mind you.