They've also built tornado, which is the sort of infrastructure that most companies would shy away from building. Tornado gave them ability to quickly build "re

They've also built tornado, which is the sort of infrastructure that most companies would shy away from building. Tornado gave them ability to quickly build "real-time" web applications, which is what Friendfeed was about. It's not a good example of "not building generic infrastructure" (Friendfeed is far from the only place doing "Comet"). The rule should be to build infrastructure when it's advantageous to do so (not earlier or later) and when it does more (or does something specific better) than an existing open source project. A corollary should be: generic infrastructure, when built by start-ups, should be open source unless it brings a distinct competitive advantage.