Mention Law & Gospel to my Pentecostal pastor friends and they would not have a clue what you mean. That is not even a category in their psyche. Our friend Steve of www.extremetheology.com has a nice introduction here.
However, Law & Gospel is not also a general category amongst new Evangelicals either. In fact in most Reformed, it is not a category too, it has been forgotten. Now why is it that in the paleo-Evangelical, gnesio-Protestant(confessing Lutheran) tradition Law & Gospel is alive and well? The simple answer is that it is written in their Confession.
Frankly I looked at the WCF and its derivative versions and you won't find Law & Gospel mentioned there, at least not mentioned in a robust thorough going way. The closest I can find is Chapter XIX of WCF. Yet this is by far not as explicit as a hermeneutic found in the BoC, specifically in Solid Declaration of the Formula of Concord Article 7 I think the erosion of this has happened in the Reformed circle because it is not written in their confession. You have to read about this expounded somewhere else outside their Symbols, unlike in the BoC wherein it is a distinct part of it and given ample exposition. When I see some posts in www.reformedcatholicism.com by Reformed folks attack this, I can only point that it is because it is not a special doctrine mentioned in their statement of faith, hence, they are not convinced of such an approach. In the Reformed tradition, you can be one without subscribing to this method, but in the Lutheran, it is not possible to be one without subscription to this teaching.
In the BoC, it is solidly declared, Law & Gospel is the way to read Scripture, why? Because it uncovers Jesus and His Cross. I am convinced that it does.
For further consideration see als Pr. Tom's Law & Gospel program.