If you are interested in testing the next generation of the ArcGIS Viewer for Flex, please join the beta program for ArcGIS API for Flex 3.0 - http://betacommunity.esri.com
This version is very similar to the recently released 2.5 but is based on the 3.0 beta 1 API which adds support for new 10.1 functionality.
Note that if you are not already part of the 10.1 beta program, and not a Flex developer, then there is not much new since the recent 2.5 release, and you might want to wait for another beta release 🙂
I use Flex Builder 4 with Flex SDK 4.1. Will this work with that? I just got an error message when I tried to build the source code around Description type Form not being found.
This quote from the beta community site may have something to do with your issue
The API is built on the Adobe Flex 4.6 platform and can be used to create browser-based web applications as well as desktop and iPhone/Android native applications.