In reply to Jeff Chandler.

Yes, I've already noticed a speed up in development time since I am able to just activate plugins rather than have to copy/paste the code into each theme functions file and then change up names to ensure it's unique to the website I'm using it on.

I used to just throw everything I could into the functions file since it seemed like the cool thing to do when building a theme, but the more I work with plugins, the more I see the benefits of having the code outside of the theme, especially when an update is done, since it goes to all client projects who used the older version of code.

Timthumb comes to mind, and I'm sure you remember how big of an issue that was when the vulnerabilities hit with it, and updating that code on every client site was an absolute pain.