I'm curious - are you folks actually using a level to check position (I note some say they do) or just eyeballing it?

It seems to me that eyeballing it could result in thinking you have it set one way, when it really isn't. Not only would there be the basic question of how accurately you can judge the angle under ideal conditions, but you have the additional problem of optical illusions created by other angles - the bottom of the seat is not straight, the top bar of the bike may be slanted, etc. Heck, even the seat top has some curve to it.

If lining the seat up with some straight line on a wall, all that may be minimized, but if not, well, I couldn't get it as accurate as I'd like.