I did the three free days of Livemocha and liked it enough that I decided to pay for it. You get a discount on a year's subscription if you pay for it during the trial period, but considering how quickly I was moving through the lessons--and considering that I don't know exactly what I'll be doing for most of the next year--I decided to go month-to-month, instead.
Overall, I like Livemocha. Several months ago I started using LingQ (the free version) to supplement Portuguese learning, and while it helped and was somewhat interesting to use, I found that it was both full of bugs and not quite what I was looking for. LingQ may be good for people who are looking for a very nonstructured course, but I don't think that's the way it presents itself, and it was simply difficult to move through. I spent way too much time just navigating back and forth in the site (and I am quite computer literate). Livemocha, on the other hand, seems to have many fewer bugs, and it's much more what I was looking for.
Benny of Fluent in 3 Months makes some great points here; I was surprised at how much I agreed with him. There's too much English--I recognize the need for some of it, especially for those with aural learning preferences. Hearing the voice say a vocabulary word in French and then English is the equivalent of a flashcard for the ears. But there are other long passages of directions or explanations that don't serve that function and waste time for me. Why isn't the "congratulations" page that turns up after every unit in my target language, at the very least? Benny also points out that the program "makes" you spend time on things you don't really need help with. I found that, too, but I didn't really expect the program to be sophisticated to that level. I don't need help with French food words, especially those that are totally obvious (the majority of the nouns I was introduced to in Level 1)--I know what baguette, cafe, and the mean, thanks.
Some of the exercises are pointless, especially the drag-and-drop vocabulary quizzes. Oh, well; I whiz through 'em.
Benny has other complaints, but he wrote his review a while ago, and it seems like Livemocha has made several improvements since then. For instance, it's definitely giving me the gender for each noun introduced, and gives both definitions and sentences of context. And I'm not sure, but I think the courses (or at least the French one) may be more differentiated for each language now. Mine does seem to be largely French-specific.
My favorite parts? I like the listening exercises. I'm more interested in understanding and speaking than anything else, so they're good for me. And while the dialogues are artificial, and I'm sure the people are speaking slowly--well, I like starting slow. I've even gotten quite curious about what's going to happen next for the two couples in the dialogues--the set who seem to be friends beginning a romance, and the two strangers who bumped into each other on the street and have spent the whole day together and are making plans for another date. Goodness, I will be disappointed if these storylines aren't continued in the next level.
The other part I think is great: the feedback. Benny mentioned that it took a long time for him to get feedback on his submissions. I don't know if it's because there are a lot more French-speakers on the site than German-speakers, but I get tons of feedback, instantly. Every submission gets at least a couple of answers within 30 minutes. Some of these are very helpful; others aren't helpful at all. (They say "nice job" or "try harder".) I'm a little tired of people telling me that I need to work on pronouncing my Rs correctly; I know that, thanks; but that's the disadvantage of having multiple people review your work. They aren't following my progress and they don't know what others have already told me. (I COULD develop my own contacts and get some consistency, though.) And I enjoy spending a little bit of time reviewing others' submissions in English, too. (On the other hand, I made one submission in LingQ, waited several days, and finally asked why it hadn't been reviewed. I was told that sometimes that happens and that I should resubmit to another tutor, which I did. Both times the tutors' profiles were active and they had good ratings. I finally got a notice from LingQ several months later--months, seriously--saying my post could not be reviewed.)
Benny's final opinion is that you can't learn a language using Livemocha, and I agree. These are, at heart, games and activities and nothing more. If I was using Livemocha as my only language-learning tool, I think I would be frustrated, because much of the material is gone over very quickly--the verbs, for instance. Or perhaps I would be not really learning anything without even noticing it, because I was passing lessons easily. But that isn't really meant as a criticism of Livemocha. I doubt there are many, if any, people who ARE using it as their only tool. So to say that it doesn't work for that is something of a straw-man. I would argue that Livemocha doesn't even really position itself that way, at least based on what I've seen--as opposed to Rosetta Stone, which definitely tries to give the impression in its advertising that it's all you need to learn a language and learn it well.
The pricepoint of Livemocha is low enough, and the benefits I'm getting from it are high enough, that I recommend it as one of a language learner's tools. I'll revisit this opinion as I progress through the levels.
Finally, I want to mention that although I'd heard of Livemocha before, it was Aaron G. Myers's Everyday Language Learner Ten Week Journey program that really got me to sign up. I definitely recommend that--get Aaron's advice while it's free. Not that he's said he's going to start charging for the Ten Week Language Journey, but he does talk about a future positioning himself as a language-learning coach, and his advice is good.