Sirmyself's page

http://www.d20pfsrd.com/magic-items/magic-weapons/magic-weapons-non-core/we apon-property---guided

This feat seems to act pretty much like the "guided" weapon property. It explicitly says a two-handed weapon damage bonus is not adjusted. Therefore, I would say this feat does the same for the attack bonus.

in my understanding, I have an evil cleric and choosing this feat would allow me to heal creatures with the evil subtype even if I normaly channel negative energy.

Actually, in The Slumbering Tsar, there's a prestige class that allows a creepy over powered critical threat range. Let's summarize how:

At 6th Level, a Justicar of Muir gains this ability:
Scourge of Evil:
-----This ability grants the Justicar a divine +1 bonus for attack and damage against evil creatures. It also doubles the critical threat range of the weapon the Justicar uses against such foes. This ability stacks with the "Improved Critical" Feat or the "Keen" weapon quality.

At 10th Level, a Justicar of Muir gains this ability
Demon-bane:
-----This ability doubles the critical threat range of the weapon used by the Justicar against evil undead and evil outsiders. This ability stacks with both the "Scourge of Evil" ability and either the "Improved Critical" feat or the "Keen" weapon quality.

So there you go, let's say your Justicar uses a Bastard Sword against a demon (evil outsider):

-----the normal critical threat range is 19-20 (Range =2)

You double it with Sourge of Evil
-----the critical threat range becomes 17-20 (Range =4)

You double it again with Demon-bane
-----the critical threat range becomes 13-20 (Range =8)

You still can double this with "Keen" or "Improved Critical"
-----the critical threat range becomes 5-20 (Range =16) (Blastin'!!)

Of course, like Dork Lord said, this doesn't mean you automaticaly touch you opponent:

Also remember that even if your threat range was 11-20 doesn't mean you -hit- with that 11 you rolled. If you still don't hit, you don't crit. Only natural 20s are auto hits. That's why I allow Improved Critical and Keen to stack in my games. It's not (usually) as unbalanced as it may seem at first glance.

but still... it pretty much means that if you touch, the damage will almost always be critical.