Living in Japan using Rosetta stone
This won`t be long.
I functionally speak Spanish, Japanese and English. I use a multiple attack method when I learn languages. Essentially I:
(a) speak a lot with native speakers
(b) do occassional grammar review from books when I make mistakes
(c) watch videos of people talking at native speed (the sources for this are endless; music videos, youtube, podcasts in other languages, tv,etc)
(d) software (ex, Rosetta stone, Mango)
(e) Audio (pimsleur, etc)
I`ve used Rosetta stone before for Japanese and German. I find it very good for practice and building vocabulary. It is also very good for testing your knowledge of grammar. Psychologically, if you are adult, you will have patterns of learning and subsequent laziness built in after many years of higher education. It is much harder for adults to do what kids do effortlessly. I use Rosetta stone to build my listening and reading skills, as well as vocabulary. Using version 3 is great. Version 2 had so many blurry pictures half the time I didnt know what was going on.
I say, if you are serious about learning languages, if you are using this program, you will need to have a multiple attack approach with at least three other influences, as well as a dictionary and a grammar book. Free audios and software run abound, and in most cities in the world there are meetup groups where people practice in different languages. It's hard to try and learn certain languages stricly from audio. You might be able to wing it with the Romance languages, but you are a dead duck if you go to languages with another subject verb structure.
I'd say use it, but only if you are seriously using a few other things to cover your bases.