While we're on the subject of .pth files, what about the idea of scanning the directory containing the main .py file for .pth files? This would make it easier to have collections of Python programs sharing a common set of modules, without having to either install them system-wide or write hairy sys.path-manipulating code or use platform-dependent symlink or PATH hacks.
I do that all the time without .pth files -- I just put all the common modules in a package and place the package in the directory containing the "main" .py files.
I do have use cases where for reasons of separate development cycles (etc.) I have some code (usually experimental or "unofficial" in some way) in a different place that also needs access to the same set of common modules, and there I use explicit sys.path manipulations. I think that even if the proposed feature was available I wouldn't switch to it -- it's too easy to forget about the .pth file and be confused when it points to the wrong place. That's also the reason why I don't use symlinks or $PYTHONPATH for this purpose. EIBTI. :-)