Colin asks the question "How do you organize your code?" and then goes on to describe the system in use at his shop.
Basically I adhere closely to the guidelines in the Patterns & Practices guide: Team Development with Visual Studio .NET and Visual SourceSafe. Chapter 3 of this guide focuses on structuring projects and solutions.
The guide recommends a single solution model whenever possible which I generally put in use with a slight modification. Chapter 3 talks about composing your source control tree into Systems, Solutions, and projects. So typically a large system might consist of only one solution, but could consist of multiple solutions. Ideally each solution is isolated from other solutions in that there are no project references from one solution to another.
However I've added a separate system called CodeLibrarySystem which contains a CodeLibrarySolution. When I create a new solution for a new system, I'll add in the necessary projects from the CodeLibrarySolution into the current system. So this breaks the "isolation" model of a Single Solution Model, but provides the benefit of code sharing. Also, by merely getting latest on my current solution, I can get all the latest changes in the code library (which really shouldn't be changing all that often).
At home and at work, I am constantly trying to refactor code so that it can be dropped in the CodeLibrarySolution as opposed to having a bunch of non-reusable code sitting in various solutions. This has worked out pretty well for me as I'm starting to have a significant code library at home. Any time I find an interesting example online, I add it to the code library (with appropriate licensing information if any).