I am among the numerous people who are boycotting Paypal because of their continuous refusal to allow setting a credit card as the default payment. I have had my checking account overdrawn on several occasions due to Paypal's greed in insisting to have the checking account charged by default (because they want to avoid credit card processing fees, of course), and their customer service is terrible in helping with these issues.
I would be happy to make a donation to Calibre if they started to accept
Bitcoin as a payment method for donations. There is no way I am going back to using Paypal.