i'm fine with little thank-you notes that take up one or two lines, but anything more than that comes off as a thank-you speech which should appear elsewhere.

as for warnings/personal experience/etc, I'd actually prefer it if warnings are separated from the author's notes section. I understand that certain authors feel that warnings may spoil the story - in that case, they can always put it under a spoiler so readers can choose whether or not to read them.

i do read author's nots anyway, but anything more than three lines of text, I skim.