Looking for some fast, simple and stable RPC library I stumbled upon MessagePack project which seems to be very good. It is also under active development.
If you used it
I'm also looking into a fast, cross-platform, cross-language, non-GPL-licensed RPC library.
From looking at the C++ source of MessagePack it seems that it doesn't work on Win32 though, which is a requirement for myself.
Except for that that single item it is on top of my list of serialization/RPC libraries.