Cool stuff. I'm working on a blog post talking about our use of Riak for Mozilla's Test Pilot project. Would be very interested to see examples of any of your MapReduce code if it is something you could share.
Sure I will extract some out in a follow up post.
Currently doing an internship project for storing and aggregating site request logs with Riak. It was hard for me to get used to all the subtle gotchas with Map/Reduce but the people on their IRC channel are very helpful and extremely patient.