How do you manage your large codebase?

Ever wondered how others manage large and complex software codebases?
- how to cope with needs to support a growing range of platforms and variants?
- what best practices to put in place to secure long term maintainability?
Dr Dobbs just published the article "Building QuickBooks: How Intuit Manages 10 Million Lines of Code" – a writeup of an interview with Jon Burt, group manager in the operations department for Intuit's Financial Management Solutions division. In order to successfully ensure consistent release of the QuickBooks solution to the market over so many years, Jon and his team have tackled exactly the above questions and many others. This article quickly went viral and generated a lot of buzz and noise – on Twitter , Slashdot and HackerNews .
Burt and Intuit is a long-term user of CloudBees Accelerator – here is a great 3m video with Jon describing the effects that faster build turnarounds have had to the Intuit large-scale development organization.
How do you manage your large codebase?