I usually will only go the manual when I get stumped on something. If it is for something that needs scheduled maintenance, say my MacBook Pro battery, or even what kind of oil my car uses, I will consult the manual for things like that. (In which case, I just go straight to the index and find the page that I need, while ignoring the rest).
I may read them more in depth if I just plain DO NOT know what to do, and also when I am bored. but for the most part, see the above
When assembling furniture however, I ALWAYS read the manual. I have had crap look like so, just because I didn't read the manual .
Most of the time the manual is an afterthought, but for some recent purchases I have actually tracked down the manual online and read it carefully before purchase. Is that sad?