A really good guide on Juggernaut (updated)

To xenocide:
The reason why I choose yasha and never upgrade it into S&Y is, comparing the 2000-gold yasha, the boost from the 2000-gold upgrade is really limited. Investing the 2000 gold into BKB would be a much better option. From my personal experience, S&Y will hardly help you win a game no matter you are a new player or expert.

I wasn't exactly advocating desolater, in fact I never get that item on any hero simply because of the investment required--just explaining why it is considered an option. My only other gripe was that SnY is far from useless. The movement and attack speed make Jugg all the more deadly, and the extra stats are primarily there to give you some survivability through HP and Armor, as well some nice damage and extra attack speed from AGI. The snare is also pretty valuable when chasing down opponents. The biggest thing about SnY especially for newer players is that it builds nicely, you can see tangible benefits while building it unlike, say, Butterfly where you spend a ton of time farming each component and don't see the big picture until it is completed. Obviously expert players know otherwise, but recommending it to newer players is hardly bad advice.

To xenocide:

If your team is winning, you can get dagon and still win the game.
If your team is losing, I don't think Deso is a good item which will help both you and your team. There are lots of basic items such as tranquil boot, ROB or Mekansm which provide armor. The -6 armor provided by Deso can be easily countered.
Remember Jugg has no stun or slow, it would be really hard for you to kill an enemy while your ulti is in cd. Also as I mentioned, it counters with most of the life steal items. It greatly limits Jugg's options. That's also the reason why Deso is so popular for naix or SNK players.

As to vanguard, it's a big burden for a Jugg to get in early game. It's true that vanguard is a good item. But with that 2000 gold, I still prefer Drum. Almost the same hp bonus and other excellent bonus, if I'm not losing too hard, I will not consider vanguard.

The rationale behind people mentioning Desolater is that assuming you land an Omnislash on a single target, 2/5/8 hits are going to apply with -6 armor on the target. Not sure on the solid numbers, but I think that's in the ballpark of an effective 20-30% increase in damage on each hit, not counting the 60 damage it also gives. Now, obviously there are a lot of reasons against it--doesn't stack with most LS items, high investment, no survivability gains--but it's not a terrible investment if you're farming insanely well and aren't against a team stacked with nukers.

Also, you have a Stout Shield, but no Vanguard or PMS listed, I feel like not getting at least the Poor Man's is a waste. 300G for the guaranteed block against heroes and the 6 AGI seems like a worthy investment.

To wilddeonpwn:

I don't quite like Deso. Unless fight against special heroes such as Alchemist, I usually would not consider Deso. It's powerful, but it doesn't stack with MOM or HOM. It will limit the build.
I forgot to mention in this guide: you can have critical strike while using omnislash. That's the reason I have Blade Dance point at lv2.

To Sp12:

Yeah, jugg is not a real "hard core" carry like void or pa. But his blade fury makes him better farmer than those real carry. Also, the damage of omnislash increases as your items getting better. If well used, it's still quite powerful in the late game.

I don't think you should ever consider blade dance that early. If not healing ward get stats.

That said, good guide. Simple and works; however, juggernaut doesn't scale well enough in the late game to carry past, say, 35 minutes unless the game has already been won. You should focus on ending/raxing rather than hard carry afk farming.