Can anyone 'prove', or even offer some evidence that Fibonacci retracement levels actually work?

I've done a couple of little tests of Fibonacci retracement levels and it appears that (on large time frames at least) they are fairly significant and therefore could be said to 'work' -

Trading Fibonacci Retracements

Trading Fibonacci Retracements II

Has anybody else done any tests that they'd like to share? I'm looking for actual evidence that these levels are statistically significant and that it therefore means something when the price reaches them. So, can anybody help 'prove' that Fibonacci retracements work?