[rkrzr]

We've been using it in production for about half a year now and it's been great. It especially shines when you have iterative algorithms were you e.g. first need to group-by something then process that a bit, then split it out again and process that a bit more etc. This kind of task is just so much faster in Spark than in MapReduce, it doesn't even compare. Also their API is much nicer and so are the underlying ideas (RDDs in particular). I think it will mostly replace MR in the future. If you are starting a new project now I see few reasons to not use Spark if it fits the bill.