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As of Build 2091, this has regressed on OSX; an open project that has no open files doesn't display the project name in the titlebar, and doesn't display the project name in the hover text. In both cases, "Sublime text 2" is the text displayed; which means if you have multiple ST2 minimized, you can't tell them apart.
This may have been added in build 2036, but it's been added in a way that (on OSX, at least) it isn't actually useful.

The issue isn't just having the name of the project displayed on the title bar -- it's having the name of the project available when the project is minimized. OSX uses the window title to describe the window when it is minimized. When you don't have a file open, it displays "Sublime Text 2". If you have a file open, it displays the name of that file.

So, if you have 5 projects open, and each of those projects have the current file as "setup.py", and the 5 windows are minimized, you can't tell the windows apart.

Therefore, the name of the current project needs to be included in the actual titlebar text, not shunted off into some side area. Honestly, if a saved project is open, I wouldn't even mind if the name of the current file wasn't in the titlebar text at all -- after all, the currently open file is displayed quite clearly in the tab bar.