"It really can be a game changer with a solid implementation. Riak is one." Can you write up a case study? What did Riak do right where the others failed? What

"It really can be a game changer with a solid implementation. Riak is one." Can you write up a case study? What did Riak do right where the others failed? What are the downsides of it, and why are those downsides more tolerable than the downsides of other systems?