We've talked about this before, but I don't think anything became of it. Here's the idea:
Create a preference so that new tabs are not created for every item clicked in the project drawer. To create a tab you would have to shift-command-click or something like that. Without the modified click, the current file would open either in a special "current item" tab on the left, that would simply be replaced by whichever item is clicked on next.
This is similar to Safari's tabbed page behavior.
For super-organized people that remember to close all the tabs they don't really need, they can choose not use the preference and retain the current behavior.
For people like me that quickly reference other files and then forget to close them, this would be a nice way to avoid unnecessary tab clutter.
Ed