Demand Progress have a petition you should sign in support of Aaron, which reads: "We stand with Aaron Swartz and his lifetime of work on ethics in government and academics.". They have also issued a statement which contains:

As best as we can tell, he is being charged with allegedly downloading too many journal articles from the Web. The government contends that downloading so many journal articles constitutes felony computer hacking and should be punished with time in prison.

We disagree.

The charges are made all the more senseless by the fact that the alleged victim has settled any claims against Aaron, explained they've suffered no loss or damage, and asked the government not to prosecute.

James Jacobs, the Government Documents Librarian at Stanford University -- where Aaron did undergraduate work -- denounced the arrest: "Aaron's prosecution undermines academic inquiry and democratic principles," Jacobs said. "It's incredible that the government would try to lock someone up for allegedly looking up articles at a library."

Aaron's record, from when he was a teenager much wiser than his years, to the present, as documented on his homepage explains his previous internet activism better than anything and is worth reproducing in full:

Aaron Swartz is the founder and director of Demand Progress, a nonprofit political action group with nearly half a million members. For the latest updates, visit the Demand Progress Blog.

He is the author of numerous articles on a variety of topics, especially the corrupting influence of big money on institutions including nonprofits, the media, politics, and public opinion. In conjunction with Shireen Barday, he downloaded and analyzed 441,170 law review articles to determine the source of their funding; the results were published in the Stanford Law Review. From 2010-11, he researched these topics as a Fellow at the Harvard Ethics Center Lab on Institutional Corruption.

He has also assisted many other researchers in collecting and analyzing large data sets with theinfo.org. His landmark analysis of Wikipedia, Who Writes Wikipedia?, has been widely cited. Working with Web inventor Tim Berners-Lee at MIT, he helped develop and popularize standards for sharing data on the Web. He also coauthored the RSS 1.0 specification, now widely used for publishing news stories.

In 2008, he created the nonprofit site watchdog.net, making it easier for people to find and access government data. He also served on the board of Change Congress, a good government nonprofit.

In 2007, he led the development of the nonprofit Open Library, an ambitious project to collect information about every book ever published. He also cofounded the online news site Reddit, where he released as free software the web framework he developed, web.py.

There is an article on Wired Feds Charge Activist As Hacker For Downloading Millions of Academic Articles, one on The Register, Reddit programmer charged with massive data theft and also one on Ars Technica, Former Reddit co-owner arrested for excessive JSTOR downloads.