Searched out for another thread. For your viewing pleasure:

I think some folks may have glossed over this link which answers many of their questions; so here it is. Careful reading should pretty much illuminate the answers to many homebrew legality queries. However, I still do not know whether trading bottle for bottle (no benefit to either brewer) is considered prohibited or not. Any lawyers or agents out there wanna field this? Interestingly, though, these laws aren't like most others in which "that which is not specifically prohibited is allowed." These laws have more an air of, "that which is not specifically allowed herein is prohibited." Serious stuff. Read it.