I very much doubt that it will ever have direct language support or even framework support - it's the kind of thing which is handled perfectly well with 3rd party libraries.
My own port of the Java code is explicit - you have to call methods to serialize/deserialize. (There are RPC stubs which will automatically serialize/deserialize, but no RPC implementation yet.)
Marc Gravell's project fits in very nicely with WCF though - as far as I'm aware, you just need to tell it (once) to use protocol buffers for serialization, and the rest is transparent.
In terms of speed, you should look at Marc Gravell's benchmark page. My code tends to be slightly faster than his, but both are much, much faster than the other serialization/deserialization options in the framework. It should be pointed out that protocol buffers are much more limited as well - they don't try to serialize arbitrary types, only the supported ones. We're going to try to support more of the common data types (decimal, DateTime etc) in a portable way (as their own protocol buffer messages) in future.
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