Mark, the hacker behind Mono's CoreCLR Security implementation has committed to SVN the support for generic code sharing.
Generic code sharing allows the same native code generated by the JIT to be reused for more than one generic instantiation. This can be done when the JIT can ensure that the code generated for the given method would be exactly the same.
This optimization currently needs to be enabled with -O=gshared
Update: Mark blogged some details and clarifications
Posted on 21 Sep 2007