Fish Tank - Tell Me I'm Crazy

I spent some time this past week digging around online and physically in ONE pet store looking at fish tanks and equipment.  I had a tank when I was younger (junior high-ish) that was 30 gallons and I had a lot of fun with it.  The Elmhurst Library has a tank and every time I take the Babe there, it is our first stop in the children's section and she goes nuts.  I figure that this might be a fun family activity: keeping a tank.  Nat thinks this is a VERY bad idea for a variety of reasons including the work involved, the upkeep, my track record on things, etc.

She's likely correct, but that doesn't mean I won't keep looking and perhaps even pull the trigger.

Do you guys have tanks at home with your kids?  Tell me I'm nuts - that this will end up being too much work.  Or...do you and your kids love it?  I think big, so 10 gallons is too small potatoes for me.  I was thinking of 30 gallons as a nice middle ground starter tank.  Freshwater, too.  I'd loooove a saltwater/marine tank, but I think you have to hire someone to care for it, right?