Watching Jack Danger's GoGaRuCo presentation the following analogy came to mind.
/lib is the asshole of your Rails application. Its fine (and desirable) for stuff to pass through there. But if you don't poop it out into nicely formed little turds we call gems eventually, your application is going to become constipated. Then you get stomachaches.
Don't constipate your app. Eat lots of roughage.