There are two known points that would cause the NCR to suddenly turn on you as some of you have experienced:

1) Getting caught installing the override chip- this will cause permanent enmity, as you basically screwed them over by doing so.

2) Screwing up while trying to rescue Kimball- if you either force your way up to the roof or get too close to the stage where Kimball speaks, they mistakenly assume you're an assassin and hate you; this can carry over past the quest, although it's not meant to.

None. Yes Man just results in unstable chaos!

If ya want something truly positive, go with House. You can't go wrong with House

Yes Man results in "chaos" ONLY until the securitrons rein in the populace. How are people conveniently forgetting this part? I'm not saying Yes Man is the best deal for Vegas, but let's actually be honest about this.

Nope. If you have a high speech score you can first convince the NCR heavies at the dam's control room to leave (thus keeping NCR non-hostile to you), then you can convince Oliver to stand down at the end.

Basically, getting caught installing the override chip will turn the NCR against you. Not getting caught installing the chip, however, will keep them on your side until the very end.

but no matter what u do at the end, trust me the ncr will be against you lol as far as after the battle.

the 1 thing that got me with the yes man ending
the 1 thing that got me with the yes man ending

If your doing a Yes Man ending, keep the B.O.S. alive.....to keep "Yes Man" in check. I wouldn't trust some A.I. in control of a city, let alone an army of robots and even manufacturing.

Imo, it should stopped being called the Independent route and called the Yes Man route. Because that's who you're putting in charge.

Try to get the best outcome for every settlement/group while maintaining their independence.
Keep the NCR as your friends by helping them out in their war effort against the Legion. If you are in good standing with the NCR and aren't detected planting the chip on the power substation you only need to convince the NCR to back down (the Boomers with bomber can help with that).
"Destroying" the Powder Gangers and the Fiends is a must. Deal with Tabitha and the Khans how you see fit, but deal with them. It's probably better to destroy the Brotherhood, though with McNamara at the head you could let them be if you don't want to kill them.

Despite all of this the departure of the Legion and NCR does attract some more raiders and bandits. Though the towns do prosper and are capable of defending themselves.

-Agree 100%.

Based on your karma vegas will be:happy and free(good),problematic and divvicult to control(neutral),an anarchic hell were people kill eachother(bad)