He told me that SOX required the company to have auditing/traceability and controls for everything. This meant they quit using any software as a service applications, they shut down IM, they have to keep track of everything on every machine, banned a whole list of applications that would interfere with SOX (iTunes, file sharing, and music app), etc.
They had to hire lawyers, more accountants, consulting firms. He told me they were looking at > 10m to comply. And that doesn't count lost productivity of having to act like a draconian big ass company where they had to have design docs for everything they do, detailed project plans, get rid of the tools they use (as listed above), etc.
In other words to go IPO now you give up agility, spend more money, and become less productive.