This is news to me, and I do wish I'd known about this a long time ago - but if you bring in more than $3k via PayPal every month you can 'apply' to have your fees reduced from 2.9% plus .30 cents to 2.5% plus .30 cents on each incoming payment.
The application is only about five questions, and approval was immediate. .4% isn't a TON of money at first glance, but it all adds up and there is no sense in paying out more than you have to!
Here's more info.
I hope this helps someone!