For the 11g client it's just not documented very well. The details of the settings can be found in http://download.oracle.com/docs/html/E10927_01/featConfig.htm, but you need to set the values in HKLM/ORACLE/ODP.NET/CLR Version/.  To get started set the TraceLevel to 1 and TraceFileName to something sensible and you get the method entry and exit points along with SQL logged.

Although not a great deal of use for solving or working around some of the issues we have been encountering with the 11.1.0.6.20 provider version (particularly problematic are support for the user defined object types and XMLType), but useful for debugging and identifying issues.