Successful grid computing
The most successful usage (from an economic standpoint) of grid computing is ubiquitous, but not obvious. The Guardian writes about it in Why did baddies get grid computing first?:
They're computing power available on demand, for the right price, if you know the right people, and can do whatever the person with the money wants: send billions of spam emails every day, bring gambling sites to their knees for ransom demands, spam blogs with comments about pharmaceuticals, host pornography and phishing sites, crack passwords[..]By that measure, the underground grid economy is worth roughly $400m a year.
(via: Sun HPC watercooler)