Our goal in the future is to open up and accept other online payment options that have lower overall fees, as well though. We definitely want you to keep as much of the money you've earned as possible, and get it as fast as possible!
Now, with increased traffic and user from things like this Show HN, we're hoping to show that we can sustain those positive early indicators at greater scale.
It would also be nice to have the option to add the fee to the invoice rather than pay it out of gross. Meaning for a $100 invoice, add $3.90 to it so that I get $100 after all fees. Most clients would never go for that but on smaller invoices you can often charge reasonable processing fees.
Certainly wouldn't work for $400+ in fees, though :)