I have/still do.
For me its not the best way of learning, but it is good for the sounds and pronounciation. It doesnt offer any guidance such as how many lessons to do at a time or in a day and if you have a question about grammar that you are confused about you have to look elsewhere for the answer.
Now most of my efforts for russian rely on books. I would recommend you look up coursebooks, maybe search a respectable university website that offers the language you want to learn and look up the course texts that it offers.
Rosetta Stone is supposed to teach the way the person first learned the language, by associating words with pictures/actions but I personally prefer learning the grammar route and then expanding my vocabulary. This depends on what language you want to learn of course, Russian/slavic grammar is easier than a lot of other languages because it follows rules, so once you learn a rule it can be applied to all the relevant words with only a few exceptions.
Also, one more point which I think is important, is that a good textbook will have sort of highlighted sections which point out certain things that are notoriously hard for learners of the language and even better, the book Im using (along with others I have seen) tell you ways the locals do it, for example in russian there are some words where almost all regions pronounce some of the letters different.
