yah i painted over areas of the lgt grill that were chrome. i think the key is preping it right.... and using a good product.
like nigel said. rock hurling at your grill are bound to happen. so making sure you have a good finish is key.
after sanding i used some plasti dip paint. lays on thick, and made for a good base. after laying on an entire can. (yah that's about a zillion coats) i used a buncha clear coat.
just dont rush it. throw back on your old grill. take a whole week, or atleast a weekend to put on a good amount of paint. doing it right the first time will save you down the road from doing it again. even with careful consideration you might need to do it again in a few years. but it beats it looking like junk the first week of winter. and not having good enough weather to fix it.