[asid61]

We use both rivets and socket head cap scews. Hex head bolts we never use. I prefer to use rivets wherever possible, generally 1/8" or 3/16" excepting the things like the gussets on the drivebase which use 1/4".
This year we used a lot more bolts because of a want to make assemblies removable, odd loading conditions that are bad for rivets, and ascetics in some places. In any situation where you're using bolts, do a weight calculation of locknuts versus 1/4" plate; surprisingly we often find that a 1/4" tapped plate is actually lighter than nuts, and that's without any sort of lightening.
Locktite is nice, but lockwashers can get the job done just fine. Our elevator back support was held on by bolts through 1x1 to 1/4" tapped plates and it never came loose due to lockwashers.
Buttonhead screws going into tapped plates also looks very good, due to the lack of a cylinder-like head and nut. I also like the increased holding area. However, for sizes 8-32 and smaller, I like to use socket head screws because the tiny size socket of button heads make it easy to strip out a screw if it's repeatedly removed and replaced.