>>6
I agree that the success rate depends on the person, but based on the fact that human memory works stronger by association combined with repetition, Heisig's books are almost essential if you want the associative aspect of learning kanji. before discovering his books, i didn't associate kanji's written form with a meaning, i just repeating the same strokes over and over in order to learn them as a meaning. what i found with heisig's method is that as long as I remember the primitive meanings of the parts, i can write a kanji perfectly without repeating it even 10 times on paper. to give you a true life story of how great heisig's method worked for me personally, when i studied abroad in Japan last spring I corrected the Japanese teacher once or twice because she wrote a kanji slightly incorrectly (mostly just forgetting a stroke or adding one where one shouldn't be) on the blackboard. people in my class must have hated me for that. but really, it's just natural to know how to write them once you know the stories associated with them.
and I also agree that kanji get easier as you learn more, and grammar and vocabulary are the biggest obstacles. you can use associative methods for learning vocabulary though. i recommend The Memory Book by Harry Lorayne and Jerry Lucas for learning how to do that. to give another real example from my life, when i first started learning Japanese, i used the associative methods in The Memory Book to learn 200 words a day (keep in mind that Japanese was my only class during the summer session i took it). The teacher called me a vocabulary maniac when I used the word "carpet" in a sentence.
unfortunately, there isn't a shortcut for grammar that i have found. grammar is basically learned through repetition. it's much easier if you live in Japan or have Japanese people you can talk to everyday. the more you use it, the better it gets, no matter what. you can't continue to speak in Japanese and get worse, even if you had that goal in mind in order to prove me wrong.
>>5
actually, i'm really lazy, so yeah, it's been about a year since i started learning. but the first week i used the book i was really gung-ho about it, so i learned about 100 kanji a day. then i got lazy and stopped, went to Japan for 4 months, came back and learned 300 more kanji in a week, and stopped again. if you are more motivated, you can learn all 2000 some in about 4 weeks. one guy who posted a book review for heisig's books on amazon learned all the meanings in 2 weeks, i think. it really is a matter of motivation, and nothing more, once you have the book.