I was sent this article earlier today about logging client side errors on the server, and I had one of those classic "why didn't I think of this before?" moments.
I quickly threw together a first draft of a jQuery plugin (and put it up on github obviously) that helps with doing this kind of thing. There's still a lot of work to be done on it, but it's a cool concept and would most certainly save a lot of developers a lot of debugging headaches (just think: no more asking people to send through their system details).
Please do jump in on github and send me pull requests.