Geek.com reports the personal assistant on your iPhone, better known as Siri, records the questions you ask her and stores them on Apple's servers. They are stored for six months and linked to a number key. Then they are deposited to a random pool of recordings for up to two years. Geek.com claims that this data is not linked to any personal information, such as a mobile number or e-mail address. Although anyone will tell you that some of the cool data search tech that the NSA makes could link all that data together in seconds.
According to Apple, the purpose of storing the conversations is to track Siri's effectiveness in providing help to iPhone owners. It is also fairly unlikely that the NSA has hacked it, like it did with Google. After all what data could an Apple fanboy have which would be remotely useful to the NSA? There are just so many Coldplay collections that the NSA is going to want to download.