I used Rosetta Stone for about a year before coming to Korea. In fact, I'm still on Level 3 of the program. I think it's a fine program if you utilize it with other material. Standing on its own, it might not be worth the price.
When I go through Rosetta Stone, I keep one page in a notebook for all the new vocab/grammar points in that lesson. Then I slowly write down each and every sentence/word that is presented and I make an English translation next to it. I make sure I understand all grammar (by referencing other books and/or asking Korean friends) before moving on.
Rosetta Stone works as a self-paced program. It's not a video game like some people treat it, where you speed-click through the screens because you recognize a word like "MAN" (mentioned in a previous post).
One of the complaints I always hear about Rosetta Stone is that it teaches you senseless phrases. I don't agree with this criticism. For example, there might be a picture of a boy laying down with a rubber toy ball on top of him. The sentence is: "The ball is on the boy." The critics say they will never have to say that sentence in real life. True. But, they learn the word for boy, ball, and the preposition "on". Rosetta Stone isn't about learning stock phrases, but about opening your vocabulary and constructing your own.
Since you're in Korea, I recommend taking actual classes. Use the native resource while you're here. Save the computer programs for supplemental study (what I do now with Rosetta) or for when you go back home.
That aside, I have heard great things about Pimsleur, but have never looked at it.
Also, have any of you seen this new Rosetta Stone? It's a fully-interactive, online version. $1000. Yikes!
--BMV