I don't know if there really is an "accurate" with exposure. What I mean by that is that the meter reads one thing and the exposure that you want might be something else. You might choose to over or under expose just to give you some options for post processing too. For example, slightly overexposing a RAW file at a higher ISO, so that when you bring it down in Photoshop some of the noise won't be as visible. Usually high ISO and overexposure doesn't go together in my case because I'm shooting in low light and doing what I can just to get a decent shutter speed and don't really have anything to spare, but it's a theory.

I try to be as accurate as I can at the time of capture, in the sense that I get my histogram close to what I have in mind. Lightening a dark shot can increase noise. I know that Noise Ninja works wonders but it's one more step and can change the look of the shot (not very experienced with it myself though). Also, if you underexpose to keep the highlights from blowing out, then lighten in PS the light areas might not look right. I don't think that a couple of blown highlights is always a bad thing.

Depends on the shot and your intention with the final look of the image and/or print. Someone told me that Ansel Adam's negatives would look horrible with straight printing because he shot his negatives to give him options he wanted with his amazing darkroom skills. I don't always shoot this way - sometimes it's just not necessary - but sometimes it helps make the final image better.