The title says it all. In a recent survey conducted by WPMU, 70% of more than 1,500 respondents from the general population in the U.S. said they had never heard of WordPress. Of course that means 30% had.
Here are a few more quick overview stats:
35-44 year olds were the group with the highest rate of recognition at 37.1%
32.1% of males said they had heard of the platform while 28.1% of females said they had
34.8% of urban populations, 26.6% of suburban populations, and 23.6% of rural populations had heard of WordPress