Botts' Dots Considered the Cause of Tour of California Stage 1 Pileup

Frank Steele of TDFblog reports that race commissaires at the Amgen Tour of California decided to neutralize the last 10 km of the finish of Stage 1 after a massive pileup that caused half the field to crash or have to stop. This allowed Discovery Channel Pro Cycling Team rider Levi Leipheimer to retain the leader's jersey despite finishing about one minute behind the stage winner.

Frank points out that the crash was caused by one of the lead riders in the field hitting a Botts' Dot, a raised pavement marker that's used as a traffic lane or pedestrian crossing marker. These markets are very common in California and are being used more and more frequently in the rest of the country.

A bit of controversy has followed this decision. This stage was neutralized at about 10 kilometers to go, at the discretion of the race referees. The current UCI rule governing sprint finishes is that crashes that take place within 3 kilometers of the finish do not affect rider placement. Some people say that the fact that this stage ended in a circuit (the course travels over the same roads multiple times) justifies the officials' ruling.

My question is, how often do Botts' Dots cause cyclists on open roads to crash? I've never hit one, to my knowledge, but I also don't think I've ever regularly ridden a route with any of these pavement markers on it.