Apparently sperm contains a lot of protein, since the sperm cells need to be good swimmers and all! So it is in fact nutritional if you manage to swallow it (but I still wouldn't recommend it, seems gross!!)...
Yuck, I would rather not though. When I was an early teen I tasted mine once, and it was because it's consistency had changed and I didn't know why or what was going on... apparently I had made it into adulthood!