> The most interesting thing I've learned so far is how clustered startup activity is in a handful of areas.

They are clustered like any other white collar company in the city, around the various historical business districts, and IMHO they could be thought as mirrors of the founder's personality to choose where they want to base their office: old downtown with cheap rents on decadent/retrofit old buildings; Paulista Avenue and Jardins with great public transportation, culture access and eclectic food; Pinheiros as the upscale cool foodie district which is now gentrified as fuck and losing its soul; Faria Lima as the core financial district; and Vila Olímpia southwards as the Faria Lima wannabe with AAA buildings but not as expensive as renting in the middle of Faria Lima.