Drush for Drupal is an awesome command line tool that allows you to do all sorts of things from a command line interface.
I recently ran into a situation where Drush started running extremely slow for me for no apparent reason. Looking at the CPU usage through top, I noticed "php-cli" was running at 99% while trying to do something with Drush and it would take 10+ seconds for Drush to finish, and sometimes it wouldn't finish at all, forcing me to Ctrl+c.
It was running fine a about a week prior so I started working backwards on the things that might have changed over the past week. The day before, I got APC up and running using CacheRouter for D6. I decided to look into the Drush issue queue for any "slow" issues and ran across an issue about adding the apc.enable_cli option for Drush to use APC. I decided to start there and actually got lucky!
Adding apc.enable_cli = 1 to my php.ini file did infact fix my slow drush problem.
If you aren't leveraging APC, then you might take a look at this post which has a few other suggestions for trouble shooting slow Drush.