I don't think most people will, and probably never if they buy an off-the-shelf PC, that provided documentation for the motherboard comes with it. I once started to read the motherboard manual, after the first page I decided I wasn't that bored, it went into way too much detail.
i look at mobo manuals when i need to find beep codes, temps, bios settings but when im building i look to find special headers to plug cables into (eg. USB/Firewire).
I generally look at it just to make sure I plug the power button, reset, hdd power light, stuff like that in correctly....generally it's on the board itself, but meh...I still like to look through the entire manual with a new motherboard...habit I guess...half the time it isn't because I need to know something, but just rather see how they've layed it out and things like that