I think there's more or less a consensus that the thinner the tubes are, the thinner the lugs should be, for fatigue reasons. Especially out at the points. To paraphrase a popular expression, flex happens - and we don't want the tube to flex over a relatively rigid lug point, which then acts like a can opener. If the lug point is thin compared to the tube, then the lug flexes with the tube and at least some of the flex occurs within the lug where breakage is unlikely.
I made a few frames out of 0.6/0.3 Prestige. (For comparison's sake, Columbus' "super light" SL is 0.9/0.6 - 50% heavier at the joint, 100% heavier in the middle) Thinned the lugs like crazy; as far as I know they're all still on the road.
There's no reason a thin lug can't have nice definition, but it takes a more skilled painter to not obliterate your work.
Mark Bulgier