It's a lot of fun, actually. I don't think I would take docking for a main course, but it's a great appetizer...or dessert. And it's something you can do in a few different ways. As MarkLondon pointed out, you can lube things up and swirl them around in there. You can also get a motion going so it's like you're fucking each others' foreskin. Cumming that way is actually pretty spectacular, especially if you can time it so you cum together.