I've written up a 2-page explanation and proof of Aumann's agreement theorem.  Here's a link to the pdf on Scribd.com.

The proof in Aumann's original paper is already very short and accessible.  (Wei Dai gave an exposition closely following Aumann's in this post.)  My intention here was to make the proof even more accessible by putting it in elementary Bayesian terms, stripping out the talk of meets and joins in partition posets.  (To be clear, the proof is just a reformulation of Aumann's and not in any way original.)

I will appreciate any suggestions on improvements.