Am I using launchpad correctly?

Only the Ubuntu entry there is related to the PPA. You're shown as active in v3c-dcom because its git branch is imported into launchpad as lp:v3c-dcom, and it's matched the commits to your Launchpad account by email address.

So should I have my projects in both the ppa and as separate projects, as seen in v3c, treedb, v3c-dcom?

My projects are hosted in SourceForge under git version control.

I'm trying to determine what these projects value-add above those in my ppa and SourceForge.

Launchpad treats each line-of-development/code tree as a separate project. While you can push different trees to the same project, branch pushes, pulls, and checkouts will be very slow because Lp only recognises the branch linked to the project's focus of development as the base for all branches. Bzr does not support nested trees, thus the project repo does not support trees without common ancestry. In summary a project is a repo for a single tree of code.

PPAs are owned b people (not projects) because they often need to contain packages from several projects. You just need one PPA to place the packages created from your projects. You do not need to use Launchpad Bugs, Blueprints, Answers, or Translations. Only Code host needs to be enabled to support build recipes.

I think you're speaking from the perspective of someone who's familiar with Launchpad.

Imagine I'm clueless about Launchpad and new to Ubuntu, and I see this guys packages in SourceForge and in projects in Launchpad.

I'd wonder why someone would put their projects in two places.

Is there somewhere on the Ubuntu website that explains the terms you're using, why people create projects in Launchpad if they host their code somewhere else, and if they do, why?

Launchpad hosts communities, not projects. Communities work with many projects, often limiting themselves to specific activities, like translations, or bug triage. 100's of sourceforge projects are mirrored in Launchpad so that they can be translated, or automatically built and packaged each day. Many are used to track bugs that affect multiple projects -- A bug in Ubuntu is probably a bug in a project hosted else where, and the root cause may be in a library, 3 affected projects and the order of the fix has to come from the root cause to the package.

There is no clear distinction between a project that is mirrored and one that uses ever aspect of Launchpad. A project might only be used by a translation community, but that wont be obvious until you try to use non-translation features.