This isn't about Rosetta Stone the stock (I have no idea where that's going), but rather about Rosetta Stone the service. For the last year or so I've used Rosetta Stone to successfully learn a new language: Hindi.
I've never been very good at languages. In highschool I tried a few (compulsory French, electives German/Latin), and based on the hours I put in and relative to my classmates, my learning productivity was pretty poor. But Rosetta Stone makes it easy. After just one year where I spent about 15-30 minutes per day, I can read (not write) and converse pretty easily in Hindi.
I think the problem with learning languages in school is that the teaching method is not geared towards actually conversing. You learn a lot about conjugating and the rules and stuff like that, but that's not really how humans best learn languages. Think about how babies learn their native tongues: we learn by doing, we learn visually and we learn by listening. Good luck teaching a baby how to learn his mother tongue by teaching him its grammar rules!
Rosetta Stone utilizes far better learning methods than what I used at school, and got me up and running pretty quickly! I was amazed how much I had learned after just a few sessions, and that encouraged me to keep going. In the end it was so easy/fun that I will probably seek to learn another language not too long from now. Even though it's expensive, Rosetta Stone impressed me enough that I would probably use it again.
For now, however, I've started learning the guitar. Any tips on the best/quickest methods to learn this instrument are appreciated!