I'm using tags for projects as well. My folders are - Next Actions, Agenda, WF, Reading, Projects, Reference and Someday/Maybe. And contexts are traditional GTD contexts.
I've found that this setup makes the project review part of the weekly review really easy. I use the All Tasks view and show just the tag for the project I'm reviewing. Then I can quickly see if I have appropriate NA assigned to the project and if I'm waiting for something. For completed next actions that I want to keep record of, I drag them to be subtasks for the Project entry (each project is in either Project or Someday/Maybe folder, preceded by "Project:" and tagged with appropriate tag).