Now that I understand the proper use of areas vs. projects, I can live without folders or nested outlines. I had been avoiding areas of responsibility and creating projects for everything, which became difficult to manage without folders.
Areas of responsibility can be used to group related projects as well as individual tasks. A project should be used for something that can be completed, such as releasing an application, or preparing for a trip. An area, on the other hand, is used for an ongoing activity such as work or blogging.
Although Things doesn’t let you simply drag an email or URL to create a task, you can still link them to the notes field of a task. The ability to sync with my iPhone and share tasks with team members more than make up for The Hit List’s nicer user interface.