According to numbers from StatusCounter, the iPad has bypassed Linux in terms of web surfing in the US, Canada, UK, Australia and The Netherlands. As a Linux enthusiast I find it disturbing but at the same time it makes complete sense.
The OS battle is between Windows, Apple and Linux. Windows and Apple dominate but Apple has a very strong grip in the market, due to its great fan/user base.
I would say, with no fear of being wrong, that most users browsing the web with an iPad, do also from their Mac[add here you preference] computer. Without playing down the quality of the product, I believe the iPad is basically taking a piggy-back ride.