Search for packages that depend on another package globally!
$ php composer.phar create-project bit3/composer-global-depends dev-master
$ cd composer-global-depends
$ ./bin/composer-global-depends.php phpmd/phpmd
[acquia/acquia-search-proxy 0.2.x-dev] require-dev phpmd/phpmd ~1.0
[acquia/acquia-search-proxy dev-master] require-dev phpmd/phpmd ~1.0
[acquia/acquia-search-proxy 0.2.x-dev] require-dev phpmd/phpmd ~1.0
[acquia/acquia-search-proxy dev-master] require-dev phpmd/phpmd ~1.0
1182 [------>---------------------] 5 secs albertofem/translatableroutepath-bundle
...