From Bootstrap to IPO?

A question for the Radar readers:

Does anyone know of a case where a company, let’s say a software or Internet company, took no institutional investment (VC or other significant investment) up until the point of a successful IPO? Let’s say that mezzanine rounds don’t count against a candidate.

This came up in conversation over the weekend, and none of the learned participants in the discussion could think of any cases like this. Is VC a prerequisite for making a public offering?