I have, in the past, used Subversion repositories to store my source documents, and followed the "project-minor" convention for repository organisation, which I have found to work very well for both large and small organisations.
We would structure our repository branches; tags & trunk as follows:
branches-+
+-personal-+
| +-alice-+
| | +-shinyNewFeature
| | +-AUTOMATED-+
| | +-shinyNewFeature
| +-bob-+
| +-AUTOMATED-+
| +-bespokeCustomerProject
+-project-+
+-shinyNewFeature
+-fixStinkyBug
tags-+
+-m20110401_releaseCandidate_0_1
+-m20110505_release_0_1
+-m20110602_milestone
trunk
Within the actual source tree itself, we would use (something like) the following structure:
(src)-+
+-developmentAutomation-+
| +-testAutomation
| +-deploymentAutomation
| +-docGeneration
| +-staticAnalysis
| +-systemTest
| +-performanceMeasurement
| +-configurationManagement
| +-utilities
+-libraries-+
| +-log-+
| | +-build
| | +-doc
| | +-test
| +-statistics-+
| | +-build
| | +-doc
| | +-test
| +-charting-+
| | +-build
| | +-doc
| | +-test
| +-distributedComputing-+
| | +-build
| | +-doc
| | +-test
| +-widgets-+
| +-build
| +-doc
| +-test
+-productLines-+
| +-flagshipProduct-+
| | +-coolFeature
| | +-anotherCoolFeature
| | +-build
| | +-doc
| | +-test
| +-coolNewProduct-+
| +-build
| +-doc
| +-test
+-project-+
+-bigImportantCustomer-+
| +-bespokeProjectOne
| +-bespokeProjectTwo
+-anotherImportantCustomer-+
+-anotherBespokeProject
The idea was (and still is) to use the structure of the repository to help structure communication between the engineering team; the customer-facing part of the business and various other stakeholders & domain experts.
To wit: Source documents that sit in one of the "project" directories get used (and earn money) only once. Documents that sit in one of the "productLines" directories earn money as many times as a product from that particular line gets sold. Documents that sit in one of the "libraries" directories earn money as many times as any of the products that use them get sold.
It makes the notion of amortization of costs explicit, and helps build support for source document reuse across the business.
In an ideal world, the customer facing part of the business would also use this structure to store presentations & other sales collateral, so developers can see what customer expectations have been created, right alongside the relevant product directory, and customer facing colleagues can track development progress on the features and products that they are selling.
It also means that there is a common structure over which our build automation tools can operate. (Our build scripts walk the source tree looking for "build" folders within which they find configuration files specifying how each component is to be built; a similar process happens for documentation generation and testing). Again, in an ideal world, the organization's website and other marketing collateral could be built in the same way.
As one final note; the continuous integration system knows that it needs to trigger a build; static analysis; smoke test & unit test run each time trunk is modified, each time any "tag" branch is modified, and each time any "AUTOMATED" branch branch is modified. This way, individual developers can use the CI system with their personal branches, an important capability, IMHO.