According to an article on TheTelecomBlog, Microsoft has patented a technology titled ‘Legal Intercept’ that would allow them to eavesdrop on VoIP conversations. From the article:

The technology would allow Microsoft to silently record communications on VoIP networks such as Skype. While some believe it’s no reason to panic, others believe it gives Microsoft or government officials a license to secretly intercept, monitor and record Skype calls while they are doing the unmentionable.

Although the patent was filed before Microsoft acquired Skype, it does explicitly name them in an example.

As for use cases:

Microsoft says that ‘Legal Intercept’ can be used by the US government or “one of its agencies”. If further mentions that this technology would require obtaining “appropriate legal permission”, which might not be that difficult for a government to acquire.

I wasn’t shocked by who may use the technology, but I am concerned if this technology is circumvented for illegal or nefarious purposes.