In a Variety article titled, "BO Falters with Core Aud," it was revealed that Harold and Kumar did 95% of its revenue in 3D.
Variety adds, "But the film had 88% of its total locations in 3D. "
However you can't tell much from that one number. For instance it does not account for how many of those theaters also had the 2D version, or the theaters that had the 2D version exclusively. In my area 78% of theaters are offering the 3D version, while 59% have the 2D version. 33% of all showings are in 2D.