Shimano is stating that their WH-7850-C24-CL and WH-7850-C50-CL clincher wheelsets may be prone to punctures due to the surface texture of the rim combined with the use of spoke-hole plugs.
The instructions for fixing this problem (basically, just use rim tape) are here.
From now on, all Shimano wheels will be shipped with rim tape, and dealers are supposed to provide you with free rim tape if you have these wheels.  This info was found on Euro websites, so it may not be an issue here in the states.
