Using ES 0.16.2 and Node 0.4.8 and recent BigDesk
$ node proxy-example.js

The issue I am facing it that the responseData of the postRequest is not valid JSON, but wrapped in jsonp.
https://github.com/lukas-vlcek/node.es/blob/master/proxy/proxy-example.js#L52
var json = JSON.parse(responseData);

I am able to remove the jsonp characters, but BigDesk does not update with no error messages.
var json = JSON.parse(responseData.replace(/^jsonp[0-9]*(/,"").replace(/);$/, ""));

On Ubuntu 11.10 with Node.js version 0.6 running the example gives:

$ node proxy.js
The "sys" module is now called "util". It should have a similar interface.

node.js:201
throw e; // process.nextTick error, or 'error' event on first tick
^
SyntaxError: Unexpected token /
at Object.parse (native)
at /home/otto/Kirjastot.fi/librarydirectory/server/lib/elasticsearch-proxy.js:179:31
at /home/otto/Kirjastot.fi/librarydirectory/server/lib/elasticsearch-proxy.js:278:9
at new (/home/otto/Kirjastot.fi/librarydirectory/server/lib/elasticsearch-proxy.js:310:5)
at Object.getProxy (/home/otto/Kirjastot.fi/librarydirectory/server/lib/elasticsearch-proxy.js:475:21)
at Object. (/home/otto/Kirjastot.fi/librarydirectory/server/proxy.js:54:32)
at Module._compile (module.js:441:26)
at Object..js (module.js:459:10)
at Module.load (module.js:348:31)
at Function._load (module.js:308:12)

Apparently node.es is not compatible with Node 0.6 as the sys API has changed..?