Ok, I see what you are saying. Maybe it makes sense if you were switching operating systems or were upgrading PHP from say 4.x to 5.x. I'd still like to see the numbers behind it though.
Also, cross-colo is not a factor of being big, it's a factor of having a BCP (business continuity plan). Every team at Yahoo is urged to have BCP for practically everything. I used to do cross-colo upgrades for a relatively small project once we had more than two frontend servers.
I think cross-colo is a size thing. BCP is good for all business, but most start ups can't afford to pay for hosting in several data centers.
I image cheap way to fake multiple colos now is to use visualization, amazon style. Heck you could do exactly what Seldo was suggesting every time on EC2.
Also, cross-colo is not a factor of being big, it's a factor of having a BCP (business continuity plan). Every team at Yahoo is urged to have BCP for practically everything. I used to do cross-colo upgrades for a relatively small project once we had more than two frontend servers.