Just as a (hopefully frustration-saving) heads-up for those of you who are more recently going through Simply Rails 2 - there seems to be a change in where acts_as_taggable_on_steroids is currently hosted - which causes some issues as you try to use the plugin as instructed in Chapter 10. While the URL to install (as instructed on Pg. 355) still works, I had some issues later on when working with the code - feedback in the command-line pointed out that acts_as_taggable_on_steroids is now hosted on GitHub before throwing some errors: githubDOTcom/jviney/acts_as_taggable_on_steroids/
If you're like me and have never used git or GitHub before, you'll need to do some prep work before continuing on in the book. Namely, you'll need to install git, which is required in order to install the plugin hosted on GitHub. For fellow Mac users, I've found the most painless way is to install MacPorts (macportsDOTorg). Once that's installed, use MacPorts to install git:
$ sudo port install git-core
Nice thing about MacPorts is that if there are dependencies required prior to installation, it will automatically install those dependencies first.
Once git is installed, go ahead and move into your shovell directory and execute the plugin installation with the new GitHub URL (be forewarned, you might need to open a new Terminal session for the shell to find git properly):
$ ruby script/plugin install git://github.com/jviney/acts_as_taggable_on_steroids.git
Once complete, continue on in the book where you left off!
Hope this helps!