Flash certainly has it's place, but I would not recommend it to any beginner. As Village correctly notes, it takes a lot of study, experience and equipment to get right, all of which a beginner is typically lacking. And of course, outside of a studio, one often does not have the luxury of carrying about and setting up the necessary lighting system that's being talked about here.
I have two kits that I carry. When I know I need everything, it's three bags. That includes 3 battery powered speed lights, my camera & lenses, my radio triggers, and light stands and accessories.
When I'm traveling light, I still have my Canon 580EX II in my main bag with a diffuser and and a 2" home depot clamp modified to attach an umbrella adapter, which is also in my main bag and is 5"x1 1/4" as well as two radio transceivers. Very compact, and sets me up with the ability to use one light off camera if the need arises.
It's difficult enough for a beginner to learn and master the controls on a DSLR. A flash only adds another piece of equipment to get right. How often do we see indoor or night time images taken with on-camera or built-in flash that results in a harsh frontal reflection or a sharp light fall-off a few feet beyond the subject matter. Think photojournalism.
Fact: The on camera flash is crap.
Fact: A cheap manual speed light will cost you less than $90 and remedy this problem, even on camera.
Fact: Most wedding photographers use a speed light on camera and achieve amazing photos.
On camera. Fall off was because it was shot outside in the dark with nothing 200 feet behind the subject. The ligthing isn't harsh, but that's because I used bounce flash. Canon's weaker flashes can expose properly @ full power up to 120 or so feet. That's pretty far and fall off doesn't become a worry until you're shooting huge rooms. There was even a picture on the Canon DSLR forums of a person lighting a gym with flash bounced off the cieling with Canon's 580EX II.
The below shot was with a $90 Vivitar. Most of my shots were with one or two $90 Vivitars as I just got the 580EX II a few weeks ago. Point it up, rubberband an index card to the back of it to help with fill flash and you're in business.
To the OP, I would recommend sticking with available light photography until you're comfortable with the DSLR. Get the fast prime lens, crank the ISO up to a sufficiently high level to achieve the desired depth of field and necessary shutter speed, set the camera to center focus, focus on the subject, recompose, and shoot. If the noise bothers you, put the camera on a tripod, or put the image through a noise reduction software like Noise Ninja.
Noise reduction software is nice and can ever be used for simple skin smoothing, but don't rely on it 100%. You lose details as it blends pixels together to eliminate noise. Too much noise reduction and your images start to look like plastic.
Below is an image that I've posted here before, and it was taken at night in the back yard with no flash and the only light source coming from that which was spilling out from inside the house. I used an 85mm f/1.8 lens set to f/2.8, 1000 ISO, and a shutter speed of 1/125'. An on-camera flash unit would have ruined the shot.
If you're talking about the pop up flash unit, then yes; an on camera speed light with a $15 diffuser could have produced the same effects at ISO 100 with an aperture of f/5.6, allowing for a DOF to capture all of the subject.
If you want to continue this conversation, I'll start a new thread instead of clogging this one up any more. It's agreed that this isn't an important issue for the OP to learn right away, but if he becomes anything more than a fairweather hobbyist, learning lighting techniques and how to control it is an important aspect of photography.
More flash photos:
http://www.flickr.com/photos/cokronk/2305893638/
http://www.flickr.com/photos/cokronk/2269161213/
