Get duplicates with LINQ

Duplicates.cs

public static IEnumerable<TSource> Duplicates<TSource>(this IEnumerable<TSource> source)
{
    return from grouping in source.GroupBy(x => x) where grouping.Count() > 1 from item in grouping select item;
}

public static IEnumerable<TSource> Duplicates<TSource>(
    this IEnumerable<TSource> source, Func<TSource, object> keySelector)
{
    return from grouping in source.GroupBy(keySelector)
            where grouping.Count() > 1
            from item in grouping
            select item;
}