Layer 7 pattern matching is one of the most powerful features of RouterOS. With it you can match almost any type of traffic and perform actions on it like QOS, blocking, etc.  The trick is writing a Regex expression that will match the type of traffic you are interested in.  I did some searching and found there are a few examples out there but not really a repository of expressions that one can draw from.  Maybe they are out there and people are keeping them for themselves but I am all in favor of sharing.  So, I am thinking of creating a site where people can contribute to a repository and everyone can benefit.  Email me if you have any ideas of how this could or should be done or if you have material to contribute.  Email sdischer[at]ispsupplies.com.