Well now you do. Because you can apparently, one guy tried it out so you don’t have to.
I don’t know what the side effects were: but bacterial infection is the first one to spring to mind. Can you get salmonella from an iPad? Well it wouldn’t surprise me, which is probably why Apple designed it for operation with hands.
In fact researching the topic, turns out the uestion was answered on US national television back in April by chat show host David Letterman when he licked the iPad on air, though to no useful effect. Why doesn’t British TV cover topics of national interest like this?