[Eddi]

i do offer this option and i can only recommend it.
it will give you a big boost in sales !!!
do it ! you wont regret it, and it is pretty easy to setup.
if you have several paysites and want to have a "join one, and get access to all sites" options, and if you run on ccbill, they will do all the work for you, however the paysites have to be on 1 server.

if you want to "join forces" with another persons paysite, its probably not recommendable at all. you have the hustle on sharing the sales, the discussion on how much content each person contributes.
the problem with the payment processor ...and so on and so on...
in my opinion its simply better to strictly seperate everything.