I donated one USD to Wikipedia a few days ago. It really made me feel worthy :)
This is the body of the email they sent me, I am adding only two CRs [carriage returns] just for the blog to look better:
Thank you for your gift of USD 1.00 to the Wikimedia Foundation, received on October 20, 2010. I’m very grateful for your support.
Your donation celebrates everything Wikipedia stands for: the power of information to help people live better lives, and the importance of sharing, freedom, learning and discovery. Thank you so much for helping to keep Wikipedia freely available for its 380 million readers around the world.
These funds support technology and people. The Wikimedia Foundation develops and improves the technology behind Wikipedia, and sustains the infrastructure that keeps it up and running. The foundation has a staff of about fifty, which provides technical, administrative, legal and outreach support for the global community of volunteers who write and edit Wikipedia.
Many people love Wikipedia, but a surprising number don't know it's run by a non-profit. Please help us spread the word by telling a few of your friends.
And again, thank you for supporting free knowledge.
* To donate: http://donate.wikimedia.org
* To visit our Blog: http://blog.wikimedia.org
* To follow us on Twitter: http://twitter.com/wikimedia
* To follow us on Facebook: http://www.facebook.com/wikipedia
This letter can serve as a record for tax purposes. No goods or
services were provided, in whole or in part, for this contribution.
The Wikimedia Foundation, Inc. is a non-profit charitable corporation
with 501(c)(3) tax exempt status in the United States. Our address is 149 New Montgomery, 3rd Floor, San Francisco, CA, 94105. Tax-exempt number: 20-0049703