This has recently been discussed:
http://talk.collegeconfidential.com/college-admissions/1807139-congressional-award.html#latest
The Congressional Award basically tracks hours devoted to public service, physical fitness, and personal development (arts, music, etc.), plus a 1 time exploration/expedition event. It’s similar to the Duke of Edinburgh award. The award levels correspond to the number of hours and duration of involvement. I personally think the main value of the award is in documenting your level of participation and commitment in 3 broad areas. Gold Medal recipients have 400+ hours of logged volunteer service, and there will be no question about their having put in the time. Meeting the required hours for someone who does music/art plus a sport isn’t that hard.
I doubt the award itself carries a lot of weight apart from participation in the component ECs, but it doesn’t hurt, and it’s a great way of documenting your commitment.