Very familiar with group buys. Have done quite a few on my cigar forum that I frequent. Last cool one was a group buy for SS SAK (swiss army knife). As stated above, it is a fair amount of work for a person to organize one, esp when you are reaching 50+ orders.
The way that we had payment were either money orders (that way you can have an address w/ payment) or paypal for "wedding gift" (+3% for fees) and a deadline to have payments in or you miss out on the group buy.
On a note...it is just tough finding something that everyone wants, can use and could get enough in bulk to buy to get a decent discount to be worth the group buy hassle for the organizer. There are also "shipping/mailing" issues that may occur and money or items can get lost in the process. Sorry, I don't mean to sound like a buzz kill, but these are things that I have seen happen with GB's in the past.
On a positive note, I love group buy's and usually participate in them esp when dealing with knives and various accessories, eventhough I am a "newbie" to this site.
Hope this helps...