Frets.com has some help.
My recommendation is to install the strap button on the heel of the guitar, so the button points mosty at the floor, instead of pointing at your belly or toward the headstock. If you install it pointing toward your belly, the "button hole" on the strap pulls directly against the button. If you install it pointing to the headstock, it might be in the way when you are playing on the 12th fret or so. When you install it pointing mostly pointing to the floor, the strap wraps around the heel, and the button hole pulls against the post instead of the button. (Look at this site: second page, first picture up is what I am talking about.
http://www.frets.com/FRETSPages/Musician/GenSetup/StrapButton/strapbutton1.html)
I have three guitars, one each way. The only time I've had a strap pull off, it was on the "point at your belly" strap button. The "point-to-the-floor" method is most secure. Two guitars came without a front strap button. With my accoustics, I couldn't take a Black and Decker to a new guitar, so I had the repair shop do it. I don't remember how much--not even $20. At least some guitars have dowels in the heel to help keep the neck and body attached. I have no idea where they are, but it is conceivable that the screw that fastens the strap button would go through one of the dowels. (I think both dovetail joints and bolts are more common than dowels, though.)
When I go to open mics, the straps on almost all of the accoustics other performers have are attached at the headstock. Before my strap button was intstalled, I used a boot lace to tie the strap thru the tuning pegs. The disadvantage of tying to the headstock is that the guitar sort of pulls to the right (the body wants to move toward your right hip), but that is not a big deal. Also, if you tie it on too close to the nut, the strap sometimes will hit the back of your thumb when you are fingering in first position.
