I recently stumbled upon this presentation of N. Zakas, and implemented the technique explained there. It is quite simple but IMHO very effective

http://www.slideshare.net/nzakas/enterprise-javascript-error-handling-presentation

the idea is to simply issue a call to a server side component (I used a .net handler but it could be a php file as well) which takes some param, log the param values and returns a 1x1 image stream back. What I like the most is that there's no need to involve ajax calls at all.

The code from the presentation is as follows:

    function log(severity, message) {      var img = new Image();      img.src = "log.php?sev=" + encodeURIComponent(severity) +      "&msg=" + encodeURIComponent(message);    }    log(1, "something bad happened");

Warning: No Longer Working!

As @JohnSmith commented below, the solution suggested here appears to no longer be functional.

An alternative to hosting your own server logging might be JSConsole.com. It's a general purpose remote debugger for JavaScript. Just register a listener, paste the script tag it generates into your page, then fire up an instance on any device. The debugger is bidirectional, so not only does the logging get forwarded to the remote console on JSConsole, you have full access to the JS environment on the remote client.