Hera's jealousy causes a whole heap of trouble for Io. Not only does Hera turn the friendly nymph into a prisoner, she later sends a gadfly (or the Furies, depending on the version) to sting Io wherever where she roams. Oh yeah, and it was Zeus's fear of his wife's jealous wrath that made him change Io into a heifer in the first place.
Hera may seem a little psycho to some people, but remember—it's not like she's paranoid or something. Zeus cheats on her constantly, and everybody knows it. There's no doubt that the queen of the gods has a pretty good reason to be jealous. Maybe Zeus and Hera should just go duke it out on Maury and save everybody else some grief.