What really surprises me is lack of some essential functionality in Finder, when one migrates from Windows to OS X. One of the things is a possibility to open an archive as a folder, i.e. staying in the directory tree and being able to drag and drop files from the archive to folders in the tree, sidebar etc.
What would you do to enable such functionality?
Update
Path Finder is an awesome shareware app, which I am going to use instead of the standard Finder (as quite many Mac users do), so I am more interested in a plug-in for Path Finder to browse archives. There is a possibility to browse packages (check the View Options), so I believe it is possible to extend it to archives. There is also a SDK for making plugins for Path Finder. The only question – how to make the plugin, so all struggling people get finally happy?
Using documented APIs, your best bet would be to wrap a filesystem, perhaps fuse-zip with MacFUSE, then associate an application with the zip UTI such that it mounts the corresponding filesystem in the Finder. You could trigger unmounting by checking for busy files and using Finder scripting interfaces to monitor open windows.