On the Mac if you three-finger tap a word, a dictionary definition appears. I'd like to know if I would be able to get this on an iPad specifically for the Japanese dictionaries.
Yes, on iPad on iOS5.1.1. At the moment, I am having trouble getting the same functionality on iPhone on iOS6.0.1, though. Japanese dictionary is there, but I can't get the English-Japanese one. Your mileage may vary, of course.