I don't use floor mats. I see more tripping over the mats than just leaving the cables exposed myself. I use cable ramps. More expensive but more professional looking and more versatile. My favorite: http://www.checkersindustrial.com/products-by-category.php?Category=1
Just my $.02....
Good luck.
Cable guards are *indeed* more professional, but at about 5-10x the cost. As for tripping, trust me, people trip over the cable guards far more often than mats :-)
The real reason for not leaving the cables exposed (as any Fire Marshall will nail you for) is because people get their feet hooked under the cable and that really trips them up, not to mention it raises the cable creating a bigger trip hazard (not to mention damaging equipment at either end of the cable). Code enforcement personnel are perfectly happy with rubber mats (even if the corners aren't taped down, which I always do).
Because of the trip hazard cable guards represent, I tend to use them only when heavier traffic is expected that might actually damage the cables. This could be heavy rolling cases (band equipment) or vehicular traffic. Cable guards are also a good idea when covering power feed cables.
The really *bad* thing about rubber mats is that they're very easy to leave behind, especially when you're employing them indoors (where the venue might already have some in place). Still, in the long run, it's cheaper than Gaf tape.
Cheers,
Randy Hyde