Livemocha is where I started learning Esperanto. I like it, mostly for the sentence structure and vocabulary it teaches, but there have been some mistakes in the translations, e.g., "salato" for "lettuce." I think it might benefit people more if either: a) they don't want to learn the grammar, or b) they already understand the basic language grammar concepts well enough to identify them.

The main problem is that, unless taking a premium course (which are rather spendy, epecially Englsih), you're not taught grammar. You could finish the Esperanto course and not know exactly what the accusative case is, only that some words have an "n" after them and some don't. You might be able to recognize the pattern if you're familiar with the concept, but otherwise, you wouldn't. I believe that they're expecting the native/fluent speakers to instruct the learners on those aspects, but I've had mistakes missed or explained poorly (or not at all), and the corrections usually occur in your target language, which can be difficult to understand if Google Translate doesn't support the language or the person write complexly. Then there are the people who either don't know their mother language or the one they're correcting well enough to correct it, or are simply too polite to correct anything (I've seen it a lot in the English "corrections").

So basically, if you're already somewhat familiar with the language you're learning or don't care for grammar concepts, I'd recommend it, especially for the fact that the units have specific concepts, like "going to the store."