What is "Anti-Alias(ing)"?

All i know so far is that if it is checked off it eases the pressure on the graphics and .'. higher FPS, hopefully. So i'd like to know what it does so i can determine for myself if i should have it on. If this belongs in Q&A then ok. Also if this has already been a topic then sorry but please link me, thanks

Someone else can probably explain this better, and I have no idea how specifically it works, but basically it smooths out the edges of polygons on the screen to make objects look more realistic. You may notice sometimes that objects will have jagged edges, and anti aliasing helps to correct that. It's especially noticeable when you're looking at something like grass, but not so much at high resolution.

http://en.wikipedia.org/wiki/Anti-aliasing

In short: it removes jags from edges.

It does have effect on your amount of FPS, so if you don't get too many FPS already, leave it off.

Thanks for that, b/c i run very high res =p

If you read any of the Wikipedia link above, you'll see that AA requires a lot of GPU processing power to calculate the attributes of the pixels. This is why your FPS goes down when you enable AA.
While playing, in high resolution, you may not even notice the "jaggies", so AA should be one of the first things you knock back if your FPS is too low. 2xAA is usually more than adequate at high rez - 4xAA is just overkill.
Also, of course, the higher the rez, the more GPU power is needed for AA, conversely, the less AA is needed for a smooth image.
(By high rez, I'm thinking 1680x1050 or more)

I run 1680x1050 with X4 AA in Guild Wars, but you are right Quaker, the different between X2 and X4 is little, but there is still a tiny difference.

But my video card can handle X4 just fine, so I'll leave it at that.

Nah. What's overkill is that 32xAA i recall hearing you can do with SLI.

Actually, I think my video card (ATI HD2900) can handle it too, but it makes the card work harder and dissipate more power (and they are power hungry enough). This seems to have an overall detrimental affect on the internal case temperatures, which used to lead to other glitches - so I leave it at 2x.

Actually though, I haven't tried using the 4xAA since my latest upgrade. But it's not as if I look at the screen and say "This needs more AA"

I'm running 8800M-GTX-SLI, and I still notice minor jagged lines at 1920x1200 2xAA on my 24" display... so, 4xAA for me!