I recently purchased a copy of "Ultimate Language Secrets," an e-book published by a guy named Owen Lee (whose real name is Owen Xia Yin) who lives in Singapore. I hesitate to write anything about this, but I don't see any other credible reviews on the web. DO NOT buy this book. Most of the content is ripped off from Wikipedia, in violation of Wikipedia's copyright policy -- this means that you can find it for FREE on the web. Lee also ripped off some of my sentences about Giuseppe Mezzofanti and a discussion of hyperpolyglots, and has probably ripped off stuff from other writers as well. I'll say it again: don't give Lee any of your money, because what he's selling isn't his.

UPDATE: Here is Wikipedia's intellectual property policy, and the reusers' guide is here. To copy material verbatim,

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

Owen Lee has put his own copyright on his book, including the material from Wikipedia, which is clearly a violation.

Here's the other problem with fixing the text from Wikipedia and calling it authoritative: Wikipedia pages change. One appendix of "Ultimate Language Secrets" is lifted from the Wikipedia entry on memory, an area in which there's a lot of research being done. Those advances may or may not ever make it to Wikipedia, but if they did, wouldn't you want to know about it?