I am not sure where I heard about this but it is really cool. You can do this in Tiger with any mouse with a scroll wheel (or scroll pea if you have a mighty mouse) Hold down the control key on the keyboard then push the scroll wheel away from you. The screen zooms to wherever the curser is. Scroll the other way and it zooms back out. This trick is great for those emails that have the really small text or websites that also have small text. You could even use it to examine photos close up for some fine tuning.