You can charge a download fee for the source or binaries. I'd sure as hell pay $100+ to grab a copy of EveryBlock and host it for my neighbourhood or city.
Basically if you release your server-side software under that license, you can get others to release the changes they make so your own hosted copy will become better (hopefully):
"The GNU Affero General Public License is designed specifically to ensure that, in such cases, the modified source code becomes available to the community. It requires the operator of a network server to provide the source code of the modified version running there to the users of that server. Therefore, public use of a modified version, on a publicly accessible server, gives the public access to the source code of the modified version."
Also, the neglect to mention the Affero GPL is sad. Check it out http://www.fsf.org/licensing/licenses/agpl-3.0.html
Basically if you release your server-side software under that license, you can get others to release the changes they make so your own hosted copy will become better (hopefully):
"The GNU Affero General Public License is designed specifically to ensure that, in such cases, the modified source code becomes available to the community. It requires the operator of a network server to provide the source code of the modified version running there to the users of that server. Therefore, public use of a modified version, on a publicly accessible server, gives the public access to the source code of the modified version."