I hope that as people are posting open content resources, they think about file formats and making the materials accessible to as many people, platforms, and devices as possible.
Wikimedia Commons has done a good job of this, using open file formats like OGG and HTML.
One concern I have is with PDF files. This has become a de facto standard for many publicatios on the web. However, it’s not a very “accessible” format. (Note: Creating these files as tagged files helps with accessibility issues, but most people don’t create their files that way, and many tools don’t even support that on the creation side.)
I’m also starting to see some of the open content portals using their own file formats (some proprietary; others open, but very specific to their particular hardware). I hope that everyone will give thought to posting files in a more open format as well so that everyone can use it.