It's unlikely sales will exceed this number, but only because Apple can't seem to crank iPads out of the factory fast enough to keep up with demand. According to Munster's study, 74% of US Apple Stores were sold out of the iPad on May 21. International stores are expected to follow the same trend: strong early sales followed by limited availability of stock.
For some perspective on the iPad's sales so far, it's worth looking at a Munster sales estimate from December of last year, about a month before the iPad's announcement. Munster then believed the iPad would sell 1.4 million iPads in 2010, at a rate of about 162,000 units per month. Instead, the iPad has far exceeded that 2010 sales estimate after only two months, and Apple has been selling an average of 34,000 iPads per day since its launch. Love it or hate it, there's no denying that the iPad has been a phenomenal success.