It is possible to do this for a specific layer through custom code but it is not possible to just switch all the maps popups to use hover instead of click or even a wise direction to consider.
I am not sure how Goggle handles this behind the scenes, but with esri this would cause a very chatty application (meaning requests to the server every time the mouse coordinates are changed).
It's a feature that some people want and there's nothing wrong with that. The problem is poor (lack of) support/implementation in the API because it's one of those things all-knowing esri doesn't think you need. The solution is a bit hackish because of this, but custom implementation is possible on a layer-by-layer basis if you are ok with using feature layers, which is a problem because IMHO they are not a fully mature feature.
