I highly recommend a perusal of Intro to Distributed Version Control (Illustrated).

From the intro: "Traditional version control helps you backup, track and synchronize files. Distributed version control makes it easy to share changes. Done right, you can get the best of both worlds: simple merging and centralized releases."

In short -- this is how we have lots of devs, and not just mark. It's a bit more work than just opening a file and changing the code, but it's really really useful.

For more information on the specifics Dreamwidth uses, check out the Dev Version Control wiki page.