Why don't you just split into two little 37signalses when the time comes?
In all the proposals / solutions mentioned here for dealing with growth while maintaining a flat culture, this is one approach I haven't seen yet. It worked well for a Dutch consultancy firm called BSO, which reached over 6000 people in the 90's, all organised into near-independent little companies of 50-ish people each, all targeting a different market, but each with the same culture and values. The firm itself was a flat company of these little companies (called "cells"), so effectively there were just 2 to 3 layers of management.
In all the proposals / solutions mentioned here for dealing with growth while maintaining a flat culture, this is one approach I haven't seen yet. It worked well for a Dutch consultancy firm called BSO, which reached over 6000 people in the 90's, all organised into near-independent little companies of 50-ish people each, all targeting a different market, but each with the same culture and values. The firm itself was a flat company of these little companies (called "cells"), so effectively there were just 2 to 3 layers of management.
(http://www.extent.nl/articles/entry/origins-original/ if you care about the details)