In reply to d_b:
Quite depends on your country and municipality, I think... Some take them (emptied, crunched open with a can opener) in the metal trash, some metal recycling lines do refuse them outright, some might put them in the "dangerous trash", it depends... Better ask yourself wherever you live (after all, there are human workers on the recycling line sorting the trash coming in, and they might just chuck them into "other trash" instead of recycling if they feel or are instructed to disregard aerosol cans and such - nobody wants their shredder to explode)
I just use a can opener (on totally emptied) canisters (works pretty well), and since our local line won't take them with the other metal trash (I asked) like beer cans and stuff, I just chuck them with some other aerosol cans and every once in a while take them to the recycling centre for "dangerous" goods. Or refill, if you feel ok about it (and know what you are doing)...