I've read through the comments and I have my own thoughts about how this will affect me and my groups. I have two groups that I moved over from Y! and took Premium over two years ago. I continue to pay for them out of my own pocket. When members found out there was a fee, they asked about making donations, and at that time I told them to wait and see what Mark worked out.
As it's been described by Mark, this won't be something we'll be using. As I explained, I'm already paying Mark every month for services beyond basic. I don't see the additional surcharge for donations as paying anything to groups.io for that.
I have two classes of members - those that might give $5 and those that might toss in $100. They guy with $5 is on a fixed income and doesn't want to see 20% of his donation got to someone else for something he doesn't see a benefit from. He'd rather mail a check. The guy with $100 doesn't see the value of giving $20 to some unknown entity for a single transaction. They both understand, and many use, PayPal and know that is less expensive.
And since it sounds like this would be a single time event, and not something people could donate to as they saw fit, it becomes a lot more work for me to have periodic regular drives to drum up donations. I know how tired people get of those public broadcasting television drives.
In the end it would be cheaper and simpler for me to set up a separate account at the bank that PayPal donations could go into, plus a monthly stipend from me, and have my groups.io payments taken out of that.