Front-end pattern libraries are hot news in the UX community these days. Anna Debenham wrote a book (http://www.fivesimplesteps.com/products/front-end-style-guides) on it and A List Apart just open-sourced its pattern library (http://patterns.alistapart.com/) for all to see.
At PebbleRoad (http://www.pebbleroad.com/) we've been giving clients pattern libraries as a deliverable. We even have our own library called Tapestry that we use to develop prototypes.
In this session, Vinay Malankad will give a behind the scenes look at how we use pattern libraries and show you how you can build one of your own!