If you are talking about those two tall and thin rectangles that are recessed into the front end, they are fake brake-cooling ducts. I feel that they are the worst part of the xB design.
i am hoping someone will make some LED for/accent lights to take up those openings...say two columns of lights with like 15 rows going down on each side, I think it would look great.
If you are talking about those two square inserts in the bumper (painted body color, about 1.5X1.5), they are covers for the tow/pull points. There is a special tool for pulling them out, and an eye bolt that you screw into the hole underneath. I was wondering that too until I saw it in the manual.
Hope someone (Toyota?) will manufacture modification kit to turn '08 xB'sFAKE brake-cooling ducts into FUNCTIONAL ducts. All it would need is removal of fake blanking panels, then add ducts to new fender-liner holes pointing at brake disks.
On my old '86 VW GTI 8v, VW offered a replacement chin spoiler from '87 16v. After I nstalled the new spoiler, VW sold me their plastic ducts that cut into the fender liners.