Version control is a key part of a successful software project, and we use Subversion heavily at Automattic. All our themes, side projects, and even PSD files go into SVN repositories.
We often talk to theme designers that are getting into more advanced theme development who need a quick crash course on using Subversion. As part our tips for version control we recommend keeping a handy reference guide at your fingertips for common Subversion commands.
Here are two great Subversion guides:
- SVN reference sheet from Cezary Sobaniec (PDF).
- Subversion Cheat Sheet, a quick reference guide for command line Subversion by Dave Child.
And if you want the motherlode, head over to the official book: Version Control with Subversion.