I didn't take part in the B&B shaving soap pass, but what I recall reading is that one member seeded a box with a number of soaps and then sent it to the next person on the list. The next person might keep the box for a few days, try a soap or two, take a few out for testing, and add a few different ones of similar value for the next person on the list. The list was settled in advance according to geography to minimize transit time and shipping charges.
IIRC, each shipment was to be tracked in case the box went astray. And, if you know you'll be out of town or unable to retrieve the box for a while, you ought to communicate that: probably most reasonable to bump someone else up into your slot and you take a later slot once you're available again. I think the soap pass was derailed for 5 weeks because a guy took a trip to the UK that was longer than expected and forgot to say anything.
Being that these are decants and samples, I'd expect people to sample a few and put them back, and pull a few that they like for further testing, dropping an equal number to replace what they took.
As for getting samples: Most retail counters have samples, but some tend to be rather stingy unless you're buying something. If you're in Neiman/Bergdorf/Nordstrom, and have just bought something, it never hurts to ask. Also: many firms will ship you samples just for asking: I've received samples from Ormonde Jayne and Frederic Malle. I mention this in case you want in but don't feel like you have much to contribute. But that said, any contributions to the box ought to be interesting, and you don't have to like it. Someone else might.
btw. Canadian members: may be a problem...iirc, customs tends to impound and destroy outright any perfume shipments.
How do you guys feel about a want list? I'd have to think that between the bunch of us, we ought to be able to fulfill a few requests.