The rationale for the decision, from the society's announcement:
... This significant decision will allow universal access to some of the most important technical research in advanced computing. In making this move USENIX is setting the standard for open access to information, an essential part of its mission. ...
Certain papers from past conferences are currently available OA from the USENIX site.
Posted by
Gavin Baker at 3/14/2008 02:42:00 PM.
The open access movement:
Putting peer-reviewed scientific and scholarly literature
on the internet. Making it available free of charge and
free of most copyright and licensing restrictions.
Removing the barriers to serious research.
I recommend the OA tracking project (OATP) as the best way to stay on top of new OA developments. You can read the OATP feed on a blog-like web page or subscribe to it by RSS, email, or Twitter. You can also help build the feed by tagging new developments you encounter.