I just found this article about how law firms value the LLM: http://www.llm-guide.com/article/534/do-law-firms-value-the-llm

Obviously law firm offices in the US and the UK don't care much about the LLM, but European law firms do. Half of the new partners that have been promoted in the Paris and Frankfurt offices of big law firms have an LLM. Not bad...

It is more valuable for a foreign lawyer.

Hope this article helps: http://abovethelaw.com/2012/01/the-value-of-the-ll-m-degree-still-low/