Convert dates to friendly text relative to the current time.

DateTimeExtensions.cs

public static class DateTimeExtensions
{
    static readonly Dictionary<double, Func<TimeSpan, string>> RelativeDateMap;

    static DateTimeExtensions() {
        RelativeDateMap = new Dictionary<double, Func<TimeSpan, string>> {
            {0.75, x => "less than a minute"},
            {1.5, x => "about a minute"},
            {45, x => string.Format("{0} minutes", Math.Round(Math.Abs(x.TotalMinutes), 0))},
            {90, x => "about an hour"},
            {60*24, x => string.Format("about {0} hours", Math.Round(Math.Abs(x.TotalHours), 0))},
            {60*48, x => "a day"},
            {60*24*30, x => string.Format("{0} days", Math.Floor(Math.Abs(x.TotalDays)))},
            {60*24*60, x => "about a month"},
            {60*24*365, x => string.Format("{0} months", Math.Floor(Math.Abs(x.TotalDays/30)))},
            {60*24*365*2, x => "about a year"},
            {Double.MaxValue, x => string.Format("{0} years", Math.Floor(Math.Abs(x.TotalDays/365)))}
        };
    }

    public static string ToRelativeDateShort(this DateTime input) {
        TimeSpan diff = DateTime.Now.Subtract(input);
        double totalMinutes = diff.TotalMinutes;

        bool useSuffix = true;
        const string suffix = " ago";
        const string prefix = "in ";

        if (totalMinutes < 0.0) {
            totalMinutes = Math.Abs(totalMinutes);
            useSuffix = false;
        }

        if (useSuffix) return RelativeDateMap.First(n => totalMinutes < n.Key).Value(diff) + suffix;
        return prefix + RelativeDateMap.First(n => totalMinutes < n.Key).Value(diff);
    }
}