I bought BS via VISA prepaid credit card which is perfect for online shopping and safe enough for me as its prepaid (im from germany).
I recently integrated several payment systems (fighting the lack of payment options - mostly cc billing, p-sms billing, voucher systems and also Paypal) and I think Paypal is one of the easiest system to integrate.
But I have HEARD that some banks add fees to paypal transactions and I think Paypal itself takes additional 13% of order value.
On the other side - even if revenue from Paypal is very low, its better than losing a prospective customer. I am sure I would have used bittorrent if I had no cc card.
It is really bad that the retail version is coming after chrismas - I think a lot of people want to play this during their holidays.