Some internet forums indicate that the instructors in one well-known vendor of the 'total immersion' method are poorly paid - 11 or 12 euros (about £9 or $18) per lesson, in Western Europe, about 25% of what customers actually pay, even though these instructors need to be graduates. So at least some of these schemes may be rip-offs.

Also, there's a rather disturbing article in Time Magazine about the similarities between the method, at least as used by some, and brainwashing:
http://www.time.com/time/magazine/article/0,9171,8...

The method of breaking people down to make them receptive is characteristic of cults, and it seems to me dangerous to attempt to force entry into the subconscious in this way. The other methods discussed in this forum (see the thread 'The Michel Thomas Method') engage the cooperation of the student fully and so avoid such danger.

On the other hand, the method of immersion as such is defended (against bilingual education) by those who use it for the US Army:
http://www.central-view.com/past.asp?number=1074

Those who believe that it is necessary to attain mastery also support the idea of immersion:
http://www.helium.com/items/238287-skill-mastering...

But should we assume that because children learn in a certain way, that such a method is automatically suitable for adults? Perhaps we should rather see the process of 'natural' learning in children as just one possibly useful aspect for a course (used in Assimil, apparently), given the greater receptivity of children to learning languages in this way, while using the reasoning capacity of adults (as more traditional courses do, including possibly Linguaphone), as well as their capacity for labour (FSI?) or exploiting previous knowledge (as Michel Thomas does).

In any case, IMHO, we need both a passive and active knowledge of a language, and so good courses will develop and exercise both.

Re: language schools, definitely check out online forums before choosing one if you care about the staff's work conditions. A friend of mine worked for Berlitz. She was paid next to nothing, not given the materials she needed to be successful, and not compensated at all for the considerable time she spent outside of class, preparing lessons. If she worked for them for less than a year (if I remember correctly), she was expected to pay them back a large sum of money for the 'training' she received from them.

Regarding the Berlitz immersion method, I am not sure what is so new about it (the article says it only started 16 months ago?) but my grandfather did a 2-week Berlitz total immersion course, about 30 years ago. It was all French, all the time, no English whatsoever, and no dictionaries allowed. I don't think the instructors were cruel in the way described by the article, though. He said it was hard and very tiring but didn't mention being verbally attacked like that.

It is true that children learn very differently from adults. I think adults can benefit a lot from being told grammatical rules to follow, whereas children are overwhelmed when given complex rules. It has been my experience with the lernu! Ana Pana course (based on learning grammar and vocabulary then reading a text and answering questions) that students under the age of 14 or so don't usually do very well in the course. Age 13 is iffy, and students at age 12 or below usually have very limited success.

I think everyone benefits from being in an immersive environment that is supportive and helpful. If you are living and breathing your target language, and must use it for every aspect of your day without being able to resort to your mother tongue, you learn faster.