I started using Rosetta Stone after having studied Russian for several years at college, but needing a refresher course since neglecting to maintain my skills. I find the software to be helpful with learning new vocabulary. As another reviewer mentioned, Rosetta Stone is somewhat like a glorified flashcard viewer. Images appear on the screen and you are prompted to choose the correct words or to complete the sentences with the correct words or case endings. Everything is multiple choice. Within the confines of that interface, it can provide decent grammar and vocabulary drills, although it does not explain the grammar rules. As there are no explanations or definitions, it's up to you to go to other sources for a more structured and comprehensive lesson plan. The drills also tend to get very repetitive as the same sentences come up over and over again, which doesn't really challenge you to use and think with the material you have learned. It's rote memorization. This method of learning has significant drawbacks and limited benefit. Like running on a treadmill, it makes you think you are progressing a lot faster than you actually are. Also like a treadmill, you might find that all your work has taken you nowhere.
Case in point: I also bought Rosetta Stone Levels 1-5 for German to try to learn German as a total beginner, and having recently completed Level 1, I can say that very little of the material has actually stuck. I tried some of the interactive online games with another German student, and my mind totally blanked. After realizing that I actually didn't know any German, I decided to retake Level 1 over again, as well as purchase some German language books online for some emergency remedial training.
To make the best use of Rosetta Stone, I would advise to go at it with a lot of discipline and most importantly, to take notes while you are working through each lesson! As repetitive as Rosetta Stone is, the material will not stick by rote learning alone. Write the words and sentences down and study them. Analyze them and break them down. Reading and typing the words, and picking from multiple choices on a computer screen is not sufficient. Also, if you don't get any speaking practice, it will be very hard to learn the language. You need to speak in order to hone your pronunciation, and you need to converse in order to gain true mastery of the language. The purpose of language is to communicate, so you can't expect to learn it if you don't actually use the language in situational contexts. That said, one thing that Rosetta Stone is particularly helpful with is pronunciation. The Russian pronunciations are accurate, although for many of the Russian sounds for which there are no equivalents in English, there is just no substitute for having a native Russian speaker who can help you. There are many language exchange sites online for that purpose.
I would not recommend Rosetta Stone as a standalone learning tool. It functions as a pretty good supplementary resource for the audio and visual aids it provides, but it is no substitute for a more structured language course in a classroom environment. That said, the reason that most of us are looking to buy a program like Rosetta Stone in the first place is because we don't have the time to enroll in a 4-days-a-week college language course.
Learning a new language is a laudable endeavor, and I truly believe that it's in every person's best interests to learn a second (or third, or fourth) language. But learning a second language, as many who have tried already know, is very difficult. For that reason, I cannot fault Rosetta Stone for making promises (as in its advertisements) to bring the languages of the world to the masses. However, learning a language is not like teaching oneself to draw. It cannot be a solitary process. To make the most of Rosetta Stone, textbooks, grammar books, and dictionaries are a must; but I also highly recommend an online language exchange site such as Livemocha, where you can practice speaking, as well as get immediate feedback on written and audio exercises from native Russian speakers. Rosetta Stone's online community is a step in the right direction, but there is never anybody online, and I find the interactive component too rigid and confining.
For what it offers, I think Rosetta Stone is a bit overpriced as each language version -- I've used Russian, German, and Pashto -- is built upon the same cookie-cutter lesson plan, which completely ignores the grammatical and cultural aspects that are unique and fundamental to every language. But if you put in the work and are resourceful and motivated, Rosetta Stone can be a useful study aid for self-learners.