I have yet to see an example of pure JavaScript code that can read an end-user's IP address. Any code I've seen returns either "localhost" or "127.0.0.1".
Bear in mind you need not get javascript to return the results of something like "ipconfig /all" to work .. all you need do is create a non SOCKS'ed connection to somewhere.
Flash is one excellent way to do that .. invoked via JS.
