This echoes the commentary in Rework that one should always monetize the things you create as a by-product of your main goal. Rework gives the physical example of Ford Motor Company starting Kingsford Charcoal to make something useful out of wood pulp waste. In the electronic sphere, Rework suggests that musicians make "making of" documentaries (a natural side-product of having to make a record) and startup founders share their knowledge gained while in pursuit of their main dreams.
Here, the same example is given with Google's bond trading (a side-product of a massive search database is a massive financial database) and similar.
I think you need to be very, very careful doing this. I know personally, I've spent a bunch of time renting co-location, which has been labor intensive, and barely break even.
It sure sounded like a good idea, as there is some money to be saved buying larger amounts of rackspace at once... but the thing is, buying more than a single rack at a time ends up requiring a lot of planning (and a lot of expensively fallow space)
Here, the same example is given with Google's bond trading (a side-product of a massive search database is a massive financial database) and similar.