In the Developer section of the umbraco ui, right-click on the Macros item in the tree view on the left. There's a menu item to import a package, which brings up a dialog box for you to either select a package from your hard drive, or to go to the Package Repository to find and install a package.
@Tony: The recently-form Package Repository Team is working to do exactly what you've described. The only thing we won't do is list "unverified" packages in an official way. The purpose of the package repository is to provide packages that are well-designed, documented (that's coming for the existing packages), and work as advertised.
cheers,
doug.
MVP 2007-2009 -
Percipient Studios