public static string ToPrettyDate(this DateTime d)
{
    TimeSpan s = DateTime.Now.Subtract(d);
    int dayDiff = (int)s.TotalDays;
    int secDiff = (int)s.TotalSeconds;
    if (dayDiff < 0 || dayDiff >= 31)
    {
        return null;
    }

    if (dayDiff == 0)
    {
        if (secDiff < 60)
        {
            return "just now";
        }

        if (secDiff < 120)
        {
            return "1 minute ago";
        }

        if (secDiff < 3600)
        {
            return string.Format("{0} minutes ago",
                Math.Floor((double)secDiff / 60));
        }

        if (secDiff < 7200)
        {
            return "1 hour ago";
        }

        if (secDiff < 86400)
        {
            return string.Format("{0} hours ago",
                Math.Floor((double)secDiff / 3600));
        }
    }

    if (dayDiff == 1)
    {
        return "yesterday";
    }
    if (dayDiff < 7)
    {
        return string.Format("{0} days ago",
            dayDiff);
    }
    if (dayDiff < 31)
    {
        return string.Format("{0} weeks ago",
            Math.Ceiling((double)dayDiff / 7));
    }
    return null;
}