I was asked to talk about my experience here.
I have used LingQ to make significant progress in many languages: German, Spanish, French, Italian, Russian, Portuguese, Swedish and now Chinese.
The only language for which LingQ (almost) was my only resource was, however, German. Sure, I did use other resources to improve my German, but only a few pages from the advanced Assimil course as well as authentic content for native speakers (newspapers, novels, etc.) after using LingQ for 2 years.
This is important because for the past 4 years, German has been the language I have been using for everyday life - for work, doctorās visits and trade school. This means that after using LingQ for 2 years to learn German, I came here, lived with a family for one year (never attended any courses here), used German every day for all sorts of things (and only German), and went on to do an apprenticeship. I take classes in economics, accounting, logistics, and even business English, French and Spanish - all in German. All of my pleasure reading and 99% of my social life is in German (the rest is in Italian or Spanish). I make deals with suppliers, solve logistical issues and have business meetings in German. Many of these things, I have never even done in English.
For other languages, I did use other methods - mostly shadowing with Assimil. The LingQ German library is simply wonderful and it was easy to learn German here. I also learned some languages before using LingQ, so it was too late to experiment.
Moving to Germany, the country I now call home, has been life-changing for me. The decision to create a LingQ account and start learning German was the best decision of my life.
I still use it to get good reading practice in French, Italian, Spanish, Russian and now Mandarin.
There is nothing to say about how I did it - I just listened and read with LingQ for 2 years, spoke about 25 times via Skype with Reinhard and Vera, sent in writing a few times and then moved to Germany. I was ready from day 1 and have never had a single problem here (although I now express myself with fewer mistakes and more subtlety, of course). In fact, when I came here, I tried to take a course to improve. I immediately placed into the C1 course and I found it too slow. I stopped after the first lesson (or maybe the second).