I build two little classes to support logging from Flex/AS3 to SOS.
The logger implements the mx.logging.ILogger interface but not the rest of the mx.logging framework as I liked to keep things in the first way.
Check the example here (right click for source). If you want to test logging directly from a website you have to start a local webserver and put a crossdomain.xml in the root. For further details read here.
Check the source directly here.
“Flex/AS3 Logging with SOS” is open source and licensed under LGPL.