I am the administrator for the Rosetta Stone contract here.
From I have been told by the librarian and the people who have used it, it an excellent program.
Keep in mind, the version that is available for the Government is significantly different from the one that is available for commercial purchase, but the lessons are identical (access is different, from I've been told by the librarian and the company).
A friend of mine is looking into buying it as well (Spanish too) - she said it was cheaper to buy like the 3 levels of Spanish as oposed to buying 1 then 2 then 3.