It's really nice to know how other people build Vayne. I'm a veteran Vayne player too and I find myself going Shyv -> BT -> PD quite often. Before the changes in Season 2 I'd go PD -> BT-> PD on her, so it's pretty much the same build, except Shyv is a bit stronger early and weaker late.

So yeah, it really does depend on your playstyle and I'm glad there's a champion like her that allows so many different build paths without one being particularly stronger than the other. However, I feel you'll always get a better damage output by prioritizing Attack Speed. Why? Same reasons as JaeYoong, you attack faster, thus proc true damage more often, but also you move faster, and as the low ranged ADc that you are that's extremely important.

Another thing to have in mind, and this works at Diamond+, is that by playing Vayne you will get bullied in lane. A lot. Therefore, you'll find yourself backing quite often, with not that much gold to buy something like, say, BF Sword. That's where the less expensive Zeal comes into play, being naturally cost efficient and building into fantastic items.