Odd question (maybe): my zoom tool was defaulting to "-" (zoom out) -- after trashing my prefs the situation reverted to normal. How did this happen in the first place? I don't see any preference settings to default to zoom out vs. zoom in.
When you select the zoom tool you have two icons, for zoom in and zoom out in the options bar. If you select the zoom out icon there.. you'll always (until you change it) have that when you go back to the zoom tool.