Vote these up:
http://brainstorm.ubuntu.com/idea/30232/http://www.reddit.com/r/Bitcoin/comments/11bj36/idea_30232_users_can_donate_digital_currency/____
Solution #1: let users 'Pay with Bitcoin' and other donation methods
In addition to the new 'Pay with PayPal' donation option that Ubuntu gives to users before the they download the desktop install, give users a choice to donate using other methods.
One desirable option would be to donate using bitcoins. Ubuntu could use many of the free software packages out there to build their own bitcoin checkout, or a bitcoin payment service like bitpay.com could be integrated similar to how paypal is currently being used. Other examples would be donating using Google checkout or credit cards.
Reference:
Canonical asks desktop users to "pay what you think Ubuntu is worth"
http://arstechnica.com/business/2012/10/canonical-asks-desktop-users-to-pay-wha t-you-think-ubuntu-is-worth/