As with any update or upgrade, I would recommend regression testing in a QA environment that has the update (UR 16 in your case) applied. That way, you can test out that the update works for your environment BEFORE you apply it to production. I would focus
on the areas in CRM that you use, that need to work properly after the update (Sales, Marketing, Customer Service).
Here is Microsoft's KB article page for what has changed for CRM 2011 UR 16. I would also recommend searching for the KB article pages for UR 14 and UR 15, so you can review the list of what has changed.
http://support.microsoft.com/kb/2872369
Good luck!