Twice. Tile both times. Once you slip and start sliding on soapy tile, no amount of clawing, scratching and grabbing is gonna stop you.
Of course, this was long ago when I was young and foolish and getting my first taste of roof cleaning from some idiot local ripoff artist.
I quickly saw him for what he was and we parted ways. Since then I've been cleaning them the right way with no problems at all.
I also knocked a ladder over once due to being in a rush. Luckily, I had my cell phone so i looked up my recently called numbers and phoned the HO inside. She came out laughing and teasing me but I suppose thats cool.
The $1000 checky in the banky more than made up for it.