I think Hadoop and M/R seem to be best for: "Take the data, transform it into another form ONCE, query the transformed using a low latency scheme many times".

I think Hadoop and M/R seem to be best for: "Take the data, transform it into another form ONCE, query the transformed using a low latency scheme many times". (E.g. building a web index or in my case, building per ad/per user/per publisher key/value pairs for ad targeting).