Not having a single rune page that you customize every game
Though I would like to be able to see my allies' runes. Let's say I'm an AD. I may want to take Press the Attack (assuming were talking about a patch where everything isn't inherently better for ADCs) for that sweet sweet extra 12% damage. But if my bruiser top lane/jungle's going to take it, I can be a bit more selfish and take Lethal Tempo for that sweet sweet AS for myself.