How can I protect laminated floor from casters on office chairs?
Replace the casters on your chairs with "hardwood floor" casters. 



These have a rubberized edge instead of typical hard plastic. Should cost in the order of USD$20-40 per chair, and takes only a few minutes at most to replace. 

It's cheaper than those acrylic mats, works everywhere (not just a 4x6' area), and doesn't look stupid (in fact you probably don't notice at all, especially if you get all black). They also make moving your chair a bit quieter.