I was cruising down the trail last night, started hearing a rubbing sound about 1/4 mile before I left the trail and crossed the street.  I stopped at the light, crossed, and the rubbing was worse.  I pulled into the parking lot of the bike shop on the corner and the tire blew the bead.  They had a tube and tire in stock, so I loaded up and was on the road ten minutes later. 

It's better to be lucky than good.