Javascript timestamp to relative time

I'm looking for a nice JS snippet to convert a timestamp (e.g. from Twitter API) to a nice user friendly relative time (e.g. 2 seconds ago, one week ago etc).

Anyone care to share some of their favourite methods (preferably not using plugins)?

Well it's pretty easy if you aren't overly concerned with accuracy. What wrong with the trivial method?

function timeDifference(current, previous) {

    var msPerMinute = 60 * 1000;
    var msPerHour = msPerMinute * 60;
    var msPerDay = msPerHour * 24;
    var msPerMonth = msPerDay * 30;
    var msPerYear = msPerDay * 365;

    var elapsed = current - previous;

    if (elapsed < msPerMinute) {
         return Math.round(elapsed/1000) + ' seconds ago';   
    }

    else if (elapsed < msPerHour) {
         return Math.round(elapsed/msPerMinute) + ' minutes ago';   
    }

    else if (elapsed < msPerDay ) {
         return Math.round(elapsed/msPerHour ) + ' hours ago';   
    }

    else if (elapsed < msPerMonth) {
        return 'approximately ' + Math.round(elapsed/msPerDay) + ' days ago';   
    }

    else if (elapsed < msPerYear) {
        return 'approximately ' + Math.round(elapsed/msPerMonth) + ' months ago';   
    }

    else {
        return 'approximately ' + Math.round(elapsed/msPerYear ) + ' years ago';   
    }
}

Working example here.

You might want to tweak it to handle the singular values better (e.g. 1 day instead of 1 days) if that bothers you.