Does it matter which way the seam (or fold) in the tape goes when taping butt joints in drywall? I've read that the seam bulge should be the side touching the wall.
That seam bulge is negligible on a newly-unrolled tape. Your butt joint should taper out 24" or more anyway, so a "bulge" of 1/64" isn't significant. It tends to flatten when the tape gets moist anyway.
You are right, some folks even trim a tiny bit off the end edge of the boards, creating a small "V", to ensure it sits as flat as possible.
I've gone over to backer boards and flying joints (in between the studs) so I can just tape all joints in a regular manner with no messing about feathering out over butts.