While you can use the app on the iPad it really is not ideal. I think developing calculators and simply using GoCalc would be easier if the app supported the larger screen and most importantly, landscape mode. I often use my ipad as a quick way to search the web, etc.. it is an extension of the desktop. My wife uses it as the ultimate laptop.. She uses while cooking, following recipes, doing finances, etc.
I think you would have a real market for GoCalc on the iPad!