Because my memories of the earlier version of Rosetta Stone are limited, and my recollection of what was actually in Dutch in 3 Months even more so, it's hard to know just how much vocabulary I've picked up. It sure _seems_ like there are words in this thing that I learned while in country -- that is, I didn't know them from the Hugo Course; I'm sure the flip is true as well (that lots of words were covered in Hugo's course that aren't in Rosetta).
I think the best part of this process for me has been re-learning the grammar in a completely different way. I'm familiar with German grammar and Dutch grammar in the way that you learn it in a textbook-driven course where the grammar is explained in the native language and the examples given in the target language. Rosetta Stone, however, buries the grammar in the examples -- there's no discussion of well, exactly _when_ do you use die vs. dat or al vs. gelegd or any of a large number of other things. Some of the forms I got purely by "ear" at first and then worked out the rule from the examples (I _still_ haven't had to break out a grammar to puzzle anything out, which I find astonishing, and grammar has NOT been the problem I have with the newspaper, either, which continues to be a combination of vocabulary and unfamiliarity with governmental institutions). But most of the forms caused the old grammar rule or trick or whatever to surface very quickly.
I have no idea what it would be like to use Rosetta Stone to learn a language that one had no (real) familiarity with. But I'm increasingly curious. Maybe in July, I'll pick a different language and try Rosetta on that.