EDIT: Additions to Masteries, Runes, and Summary

EDIT: Have not played Yorick since the buffs will update soon.

EDIT: Yorick no longer requires stacking damage to carry late game, also has no mana problems at all. If the game goes long enough i now sell Tiamats for either a Bloodthirster or Atma's depending on teams AD/AP damage.

EDIT: Fixed skill sequence mistake

I wanted to share this build I've been working on since release, and while it is still a work in progress, i have had much success with this build. It is nothing like any of the other builds I have seen or heard suggested. I always wanted to take control of his burst and use it to my advantage, yet continually obtained only assists as i could not hold enemies still long enough to get the kill alone, if at all. After working on this build since the day he was released I have come to the conclusion that Yorick is NOT tanky... He can actually be a very scarey toon which can push lanes and towers like crazy. He is an amazing roamer and ganker with his fantastic burst, and he escapes very well too.

Pros:
Yorick is a great roaming ganker
He can dominate a lane, or easily solo a lane vs 2 enemies
His burst is amazing
He tells a good joke

Cons:
Difficulty closing distance against multiple ranged opponents
Will never get a date

I have used a combination of Ghost and Flash or Exhaust since release, I can't say really how useful others would be but I can say that Ghost is a must have. This is your early kills enabler, early kills grant you your +attack damage earlier and begin your giant snowball. Flash is mainly something to help you escape multiple enemies or close quickly for a gank.

The bigger the burst the better, it improves your abilites also. This helps you dominate lanes and harrass the enemy very well. It is also what makes you an awesome roaming ganker afterward. Your mana is somewhat low and while mostly a bigger pool is better we opt instead for better regen in the begining. We also reduce our cooldowns as only 1 item I would ever chose to build on Yorick improves cooldowns and that is The Brutilizer and upward from it. Cooldown is important for your bursts, by level 18 you should be able to burst 3-4 enemies before running out of mana without the blue buff. I have also tried magic pen runes for much greater harrassment, this works but involved building a completely different way which i will add as another build later on. I started out using +dodge seals, these worked well but in order to solve his mana problems I swapped them out for flat mana regen, flat because honestly early game is the only time you have a problem.

The skill sequence; No points in Q till 5, your W and E are essential for harrass and sustainability. During the laning phase your W and E are KING, allowing you to harrass enemies till they cry, and kill unwary enemies under their tower. It also allows you to farm like a madman, especially once you have your Tiamat. But most importantly, using your mana as little as possible they will allow you and your partner to stay in your lane pretty much as long as you want. The slow, lifesteal and damage output by these 2 skills is crazy. Yorick can even push the right 2 enemies tower alone. Yoricks Q is great once you have Sheen and some attack damage up your sleeve. Always remember not to spam your skills at an enemy too quickly, allowing your auto to proc Sheen between as many abilities as possible, it proc's every 3 seconds so you can get it to proc 2-3 times in a 1v1 fight.

Item build revised after buff. It is concentrated on giving Yorick a much better early game. Im not sure i would mid with this build as it may lack mana early game to sustain laning, however it does harrass like a boss. I will update this later on I think.

Ive nearly run out of time so a quick summary of Yorick the Snowball; Always remember, Yorick is a high damage bursting fiend. harrass your enemies constantly, try to lane with a ranged partner and you will have their tower by 6 easily. You can dive enemies on 2 or less bars with your W and E, forcing them to b or getting kills even. Once you have your tower down, roam. Take red, and blue once you have sheen. Ganks need not be co-ordinated with allies as, they will succeed 9/10 times anyway. Always remember to buy your attack damage components to items first, these give you the most benefit, not just for farming and ganking, but for surviving as well. You will do REALLY well with both blue and red buff, reducing cooldowns for your sheen proc and healing, red for its bonus damage. As I am often roaming I like to steal my enemies buffs, Yorick can kill them VERY quickly once you obtain Sheen. Blue buff will allow you to unload your burst every 2-3 seconds upto 8 or 9 times.

This is all I have time for at the moment. I will add and improve upon it as often as I can though. If anyone else uses a similar build and has suggestions pls let me know and I will give them a try :) Thanks.