It'd be nice if one of the JS benchmarks actually POST'd the results back to the server, with current browser, and had a UI that allowed comparing the results for different browsers on different tests.
Both Kraken and Sunspider provide results in a form that you can copy and paste, and a UI for comparing results from different browsers. (But they don't let you view results from previous users, which I guess might be what you're asking for.)
Also, given the number of 'fans' on the Internet, I suspect that such a tool would have serious issues with users tweaking the benchmark and uploading fake data.