Weaving is certainly legal, but the question of fairness is certainly debatable. A quick shuffle does randomize the cards though you end up with a much greater chance of spacing combos. In a Championship tournament I would certainly do a triple sorting and then three set of halves shuffling the same way I ensure my cards are randomized before and after a game to prevent clumping of cards. (Those words may not mean anything to anyone else, but it is quite an excellent way to force cards through a deck).