I'm a concert photographer, and Jeremy makes some good points.
However, I still use my camera's light meter when shooting, albeit a bit differently than you might expect. I've set my camera body to manual shutter speed and aperture control, but have auto-ISO turned on. That way, the camera automatically boosts or decreases the ISO, depending on the amount of available light.
Different focal lengths however have different effects on your exposure metering. For instance, I tend to dial in a -0.7 stops exposure compensation for my 50mm lens (fixed focal), but a whopping +1.3 for my 10mm fisheye (extreme wideangle).
You'll have to live with the fact that your metering system will mess up as soon as you are in the direct light of a backlight spot, something you can only compensate slightly with spot metering (I use matrix metering with spot metering mapped to a seperate button).
As far as autofocus goes, I use that mode that's like single point AF, but which sometimes "borrows" data from surrounding AF points when your subject suddenly moves out of your composition. It's the second mode from the bottom upI think.
That way, I always know where I'm focusing, and my lens doesn't hunt as much when the artist moves to fast for me to track.
Still, even with comprehension of all this techno mumble jumble, the D3000 with an 18-55 is not very well suited for concert photography (especially not the smaller gigs). I'd recommend you get the new AF-S (mind that "S"!) 50mm F/1.8, or if that's not available, the 35mm F/1.8.
I've just gotten back from 3 days of concert shooting, and building stages/festivals, with next to no sleep, so excuse the spelling errors.
P.S. In a perfect world I'd be shooting at 1/250th all the time, but the simple truth is I really don't have sufficient light (the fate of a concert photographer). I tend to find 1/80th is quite acceptable, especially for "microphone" shots. For obvious reasons, this will not as well for jumping punk rockers.
I take pictures so quickly, my highschool was "Continuous High".