I absolutely love this guide, using it as a starter when I first started playing Yi, it helped me a lot, especially learning the mechanics of the game, as without it I probably never would've realized how valuable a neutral creep buff really is!
In public games, 75-80% of the time I end up heavily carrying my team through mid-game ganks and backdooring, usually accumulating atleast a 1.5 KDR, (over 3.0 in my last game, 21-6), and I find the ability to adapt from this guide amazing. I've changed the item build quite a bit, shying away from crits and more onto atk speed and life steal.
Lately, my typical game and item build has been as follows:
Long Sword + Health Pot
Pill back for Madred's Razor + Vampiric Scepter (Sound familiar?)
Jungle for Lizard Buff
Attempt ganks and help out lanes.
Get boots of choice, if there are disablers, get Mercury's, if not, Swiftness.
Work towards Phantom Dancer (Zeal first, Sword of Divine if Jax is giving you trouble)
Work towards BloodThirster or the Aura one (forget name D: )
This is where you choose what you need, if you're having trouble with bulk, get SunFire Cloak (Warmogs if it is really THAT bad, but you shouldn't be the one that's tanking), spell bulk? Banshee's Veil. Usually games don't last this long for me, but if so, I've usually been fed enough to get Infinity Edge, if I'm not doing well, I figure out why and choose the item to remedy it.