Look down at all the Vayne players that still build zeal as their first buy. Bf sword is so much better, more AD = more lifesteal and easier CSing and BF sword does more consistent dmg; zeal relies too much on crits and will only do more damage if every auto attack crits and a fight is prolonged for more than 10 seconds.
But yeah, I barely build GA at all, but in a lot of my games I just get jumped on by every single champion (Jungle, mid, top, support, errybody) so GA has to be a must. Mercurials is my most popular buy, banshee's is shite. Deadman's plate is good too, try it sometime.