Overall judgement: I value each chapter of T4BBC as approximately equal to a well researched lukeprog post on the given subject matter. Tim's chapters tend to be well researched (relative to the genre of science popularization) and based on a mix of academic research, practices of prominent trainers and some findings from (systematic) self experimenters.
Personal experiences: I followed the diet and experienced significant improvements to cognition and mood as well as the obvious changes to body composition. Because carbs really do suck in the doses typically consumed.
The exercise routine (for mass gain) worked well for me. By which I mean about the same results as my typical gym experiences had been but in less time.
I think comparing Feriss to lukeprog's posts does the latter a grave injustice.
In the matters I consider myself fairly knowledgeable, like spaced repetitions, the claims lukeprog makes are consistent with what I expect. In matters I consider myself fairly knowledgeable like polyphasic sleep, the claims Feriss makes are not consistent with what I expect, to the point where I wondered if Feriss had ever actually done it as he claims or whether he was just plagiarizing things others had written. (I'm not impressed with what he wrote about the Zeo either.) And Gerard above discusses the ECA stack.
I've just read the Four-Hour Body by Timothy Ferriss. It seems on the face of it like ridiculously valuable material, if true - like what the completed version of Michael Vassar's proposed reboot of dietary science would look like at the finish point if dieting turned out to be more susceptible to Munchkinism than in my wildest dreams. Ferriss also talks the rationalist talk quite well in this book, much more so than in Four-Hour Workweek; he cites the experiments and occasionally says things like "I spent a lot of money on this and I expected it to work and it didn't work at all" or "I tried this and it seemed to work and I have no idea why it worked and I think it was probably a placebo effect."
Does the LessWrong hivemind have an opinion about 4HB? Has anyone tried it and found that it doesn't work, or that it does work, or that it works but not as well as Ferriss thinks it should work?