JavaScript time between dates

A person asked a question in my post about sorting dates in Javascript, basically on how to return a measurement of time between dates, such as days, hours, minutes, seconds. I haven’t really ever had to do something like this so I figured I would see if it was as easy as I assumed it would be in JS. This is what I came up with.

var dob = new Date("9/28/1982"),
    today = new Date("9/21/2010");

// Days between dates

// Years between dates

Returns pretty accurate results, Im not accounting for leap years so it thinks I’m already 28 even though I still have a few days to go.