I think I finally understand what makes Vayne tick. And this thread is both to share this knowledge, and to also verify with our AD-carry experts if the following is correct.
(actually, the 2nd point is why I am bothering to type this in the first place. Can someone check if I am correct?)
The key is, and has always been, Vayne's silver bolts. It does a metric ton of damage. And that's TRUE damage. And that's ENEMY HP % True damage. In just 5 procs of silver bolts, the % TRUE damage and the Flat TRUE damage can add up to anywhere from 40% to 50% of an opponent's HP, depending on how squishy he is.
Porcing this skill by hitting 3 times is the (obvious) key to use Vayne.
The TRUE hidden key (IMO) for Vayne is this: you can porc silver bolts quite often even without a single attack-speed item.
Of course, by the end game, you should have attack-speed items (that goes without saying), but before getting even one of those attack speed items you should still be able to produce quite an amazing amount of rate-of-fire. This is especially important during the laning phase and the mid-game (both phases which I used to struggle all the time, and thus fail with Vayne in the past)
This rate-of-fire is improved by using her skills. Both Q and E are attack abilities that porc silver bolts, and Q is both spammable AND resets your attack animation AND repositions/chases to attack more (especially note that higher levels of Q has even less cooldown).
Or: Q enables you to make sure you can shoot the opponent, it also enables you to shoot the opponent faster if you use it immediately after a normal shot leaves your crossbow. And it is quite spammable, thus making sure you shoot faster all the time. And E also helps add another silver ring onto the opponent AND can be used as an interrupt too...
... and all the combo attack-cancelling stacks damage like crazy: not only silver bolts is porced and porced often, Q and E both stacks quite a lot of bonus damage on top of that.
Remember to watch your mana thou. Spamming skills as such tends to burn out your mana quite quickly, especially in the laning phase.
So, i think the following should be done for Vayne players:
Skills
Prioritize the skills as follows:
Q-W-E for the first three skill points, then followed by maxing W (silver bolts), followed by Q then E. (obviously, R should be taken as soon as you can take it)
Items
Get survivability items and boots in the early game (2 or 3 Doran stacking), since all your early damage is going to come from high-leveled (or max leveled) Silver bolts anyways.
Get a BFSword right after Doran stacking, as Doran's alone provide absolutely crappy damage. Silver bolts may cause a lot of damage, but high normal damage can't hurt.
Get level 2 boots next. Attack speed boots are not a necessity, either movement 3 boots or tenacity boots will be good enough. (Tenacity boots obviously depends on the opponent...)
Then build one of the standard big AD damage items using the BFSword as appropriate (I usually go for Bloodthirster as the first item, as the lifesteal is a nice complement to high amounts of True damage from silver bolts).
Followed by a maybe: depending on how hard the team is being snowballed, build a PD or other attack speed item now... or later. The above reasoning on attack speed is why attack speed items is not an absolutely necessary step so soon after your first big damage item.
No matter your choice in (not) building an attack speed item, it is pretty obvious you'd be going for a second standard big AD damage item after. Note that this is (perhaps?) what makes Vayne scary: loads of early damage, and thanks to the skill's attack reset she is not lacking in attack speed.
Lastly build survival items again as my last one or two items, as the Dorans should be long sold off by then.
Strategy
During laning, harassing is pretty simple: hit 3 times, or don't bother.
You can do this by either hit-Q-hit-hit, or hit-Q-hit-E. or any combination of. Note that if you can pin an opponent to the wall... it means your opponent is stupid enough to let you do so (the lane is pretty wide)
Mid-game is just like early-game, but try to use E to knock an opponent into a wall especially if in the jungle as that will stun them for a significant amount of time... thus giving you quite a bit of time to shoot and proc Silver bolts en-massed. If undisturbed and using Vayne low-cooldown ulti at the same time, it is quite possible to remove huge chunks of hp within a short amount of time without any retaliation, even if the pinned enemy is a tank.
During late-game... you have attack speed items. Use Q only to get/keep in position, R often if you think you're going to spend a lot of time standing on one spot shooting (it cooldowns fast enough for you to "spam" it), and just auto-fire away. E is still used as mid-game.
So, comments?