Most of the Fortune 500s have enough data to theoretically have something to throw M/R at, though whether they'd gain from any particular project is anyone's guess.

e.g. At a national bank, determine whether distance to the nearest branch or ATM correlates with deposit frequency or average customer relationship value. Your inputs are a) 10 billion timestamped transactions, b) 50 million accounts, c) 200 million addresses and dates for which they began and entered service, and d) a list of 25,000 branch/ATM locations and the dates they entered service.

This is fairly straightforward to describe as a map/reduce job. You could do it on one machine with a few nested loops and some elbow grease, too, but the mucky mucks might want an answer this quarter.

I know the feeling, though: I keep wanting to try it, but haven't been able to find a good excuse in my own business yet.