In spite of M&M's slanderous guess, I did in fact open the beer can prior to cooking the chicken. I did not, however, drink enough of the beer prior to putting the chicken on top of the can. I won't make that mistake again.
The end result? My wife smelled it first and I went out to check, about 10 minutes after I put the meat on the grill. Smoke was billowing out, and the temperature guage showed more than 500 degrees. I made a quick assumption that opening the grill might be dangerous, so I just turned off the burners and walked away for a few minutes. When I opened the grill, the flames were still burning on the legs. Well, on what was left of the legs anyway.
I was able to salvage more than half of the meat.