I see these tires-turned-planters all over Brooklyn, and I think they're fantastic. Recycling tires is a full-fledged environmental problem, one that has spawned businesses and government initiatives. These planters aren't the global solution, but they're a fantastic localized re-use. Sure, they might not be the safest things in the world to grow food in, but in terms of brightening up a street with flowers, they work as well as anything. I particularly love the way they sit on the rims off the ground (my garden-savvy friends explain that the rims' original holes are excellent for drainage), and hold bright paints well (though the photos don't showcase any of those).
Directions on how to make them can be found here, with some more elaborate ideas here and here (though I've never seen the latter in Brooklyn).