Is there a way to search for Hackage packages that depend on package X (for any package X)? It would be great to find examples of how a package is used in the wild to get an idea of its capabilities. (Also useful for [attempting to] resolve cabal hell.)
Note: it looks like http://packdeps.haskellers.com/ is looking for a new organization to care for and feed the service. In the meantime, try https://hackage.haskell.org/package/packdeps, if you can convince it to build.
You can use Michael Snoyman's packdeps. For example, this link will tell you all the package that depend on the package text. You can just edit that link with the package name to get the reverse dependencies.