To those who may not read RoG, (a vastly superio blog, to be sure), a recent blog series of item choice analysis' by VVinrar has recently caught my eye.
And google the rest of the stuff
ADC's usually have a pretty generic kit... a couple of steriods, an escape, some utility and AoE. Instead of focusing on abilites, they focus on other aspects of gameplay, like DPS, positioning, and prediction. This means that Item choices are much more important on ADCs than on any other role.
I highly recommend ADC read the stuff by VVinrar.