Apple Chief Operating Officer Tim Cook said Tuesday that the iPad market is “very big” and speculated about cannibalization of PCs, while two market research firms upped their forecasts for tablet shipments in 2010.

During Apple’s third-quarter earnings conference call Tuesday, Cook mused about the continuing strong sales of the iPad and its potential to eat into PC sales. The iPad “is not following typical early adopter curve and taking a long time to cross into the mainstream…We are absolutely selling every unit (iPad) that we can make,” Cook said.

Cook continued. “Our guts tell us that this market is very big…if it turns out that iPad cannibalizes PCs, that’s fantastic for us because there is a lot of PCs to cannibalize,” he said.