SVN rev 166 (bitcoin version 0.3.13.4) implements secure incoming SSL JSON-RPC connections to bitcoind or bitcoin -server on Linux and OSX.
I've created a wiki page with detailed instructions on how to configure bitcoin.conf for SSL JSON-RPC connections.
SSL support is enabled at compile time with the USE_SSL #define, and is not enabled in the Windows makefiles because I'm told there are... issues... compiling full OpenSSL libraries on Windows (core bitcoin uses the openssl libcrypto library, this change requires the full libssl library).