I think that Duolingo and Babble could be a good way to START learning a language but not very useful once you are a little more advanced. I tried Babbel and chose "advanced" but it was still very simplistic for Spanish and with Duolingo once you know enough synonyms or your language is advanced enough it's too boring even if it "should" make for a nice review. Even in the reviews and complaints of Duolingo it's common for people to say that once you get further along there are many mistakes or problems because not enough people get that far in order to have those things corrected. 

My review is that if you are just starting out these kinds of software programs can be very useful but once you are past the beginning stage they can be frustrating and annoying or boring. With Duolingo you can see the answers before typing them in which is very useful for a rank beginner. Once you are past the very beginning stages though, then I think there are better courses with which to use your time and efforts. 

In my opinion it`s quite ok. I am interested in the process of translating texts and how people develop such online language lessons. The incubator ( common people who act like "experts" and create lessons for the other users) is pretty interesting but nobody answered me yet and nobody accepted me in one of those incubators so far. I guess they only take people who really are pro`s in the language which is actually good lol but I am upset because I am really interested in it.

I like the translation practice. Of course, there are many people working with the same text and that`s why there are a lot of corrections of your version. Some of those corrections are completely good (considering that there is no German-Spanish combination but only English-Spanish and none of it is my mother tounge) but some people just correct it even worse and I notice it even if it is not my native language!. But that`s not a big problem for me since I just want to get a feeling for a translation and there is a big amount of people who have a brilliant own version of the text.

If you are a complete beginner, I would not recommend this page, or rather - don`t use this site as your only source because there is no real explanation of the grammar etc. and it still contains some mistakes like Liza has said.

I think Duolingo is an excellent tool to add to our ever growing language learning toolboxes.

I have mixed feelings about this. I use duolingo when I just started to learn languages (French and Italian). The basic stages are useful. And it helps me to expand my vocabulary. However, as the stage gets more advance, there are sentences that are quite complicated to translate (which is completely understandable, given the nature of a learning process). And this is where I started to find problem as the application focus more on the grammar of my English translation, even minor one, rather than on my comprehension. I understood very well the meaning of the French sentences, but my lacking in English (or lacking in attentiveness, that is) set me back. So I kept loosing hearts and never finished a language tree. But I still use it every once in a while. 

I like Duolingo. I agree with Peachey with audio and grammar. I study English and Portuguese. What I like is that you can correct questionable phrases in your native language, I had problems with that. Some phrases in Spanish you can say it in different ways and Duolingo accepts one translation.