I don't know if anyone's using Erlang's binary serialization format per se, outside of Erlang programs; but BERT (Binary ERlang Term) is an Erlang-compatible binary data interchange format and RPC protocol specified and open-sourced by the GitHub guys. It's based on and fully binary-compatible with the Erlang external term format.
As you can see on the BERT website, there are implementations in a number of programming languages, including C++, JavaScript, Ruby, Python, Scala, Haskell, Go, Factor, Scheme, Clojure, and Common Lisp. The mailing list currently has 85+ members subscribed to it, so quite a few people are indeed using BERT, and hence indirectly the Erlang binary format.
In my own use, mostly in Ruby and Common Lisp applications, BERT has proved useful as essentially a binary form of S-expressions.