Seriously? I've been contemplating selling mine. I have a seriously nice RO/DI that I used to use in my reefkeeping days. For coral reefs, nitrates and more importantly phosphates are a horrible thing to add during a water change. RO/DI was the best way to make sure that nothing like that got into your tank.
In the planted tank world, nitrates and phosphates are something you dose often. I figured that using tap water would be good for planted tanks. No?
I guess it depends on your source water.