I want to start out by saying this is my own personal opinion. Some people say they are glad they got the kit lens, while I was sooooo glad to stop using it when I made my 50mm purchase. My kit lens hardly ever gets used. If I do use it, I have to use my speedlite. So if you get a kit lens, make sure you have either the Light Scoop (nice if you're on a small budget, it's only $25) or a Speedlite (more control, higher power, but more expensive), so that your flash isn't pointed forward and you can bounce it (more pleasing look). You want to avoid the pop-up flash at all costs.
Okay, so take a look at that chart. This would be some of the different apertures you can shoot at, depending on your lens. The gray area is the opening in the lens and how much light can pass through. Quite the difference, isn't it?
The 18-55mm kit lens has a variable aperture of f/3.5-5.6. What does this mean? It means that when shooting at 18mm the maximum aperture you can shoot at is f/3.5 while on the 55mm end you can only open up to f/5.6. Looking at the chart that's not going to let much light in compared to f/2, is it?
When you get fast glass (f/1.2, f/1.4, f/1.8, or f/2 for primes - f/2.8 for zooms), you're allowing yourself to use faster shutter speeds (less motion blur/camera shake), keep your ISO down (less grain), and even shallower depth of fields if you wish.
Not to mention you get what you pay for. The kit lens isn't good quality. You pay all this money for a nice camera and you get the kit lens? Primes are faster and sharper. Usually the more you pay, the higher the quality. Canon has L series lenses. These are their professional quality lenses and are all-around better lenses (build quality, sharpness, vignetting, smooth bokeh, SOOC colors). Nikon has professional grade glass too, except it's not labeled like Canon. You don't have to spend thousands to have a great lens though. I currently don't have any professional grade glass (hope to soon though), and I have a lot of high quality photos.
I LOVE both my 50mm f/1.8 and 85mm f/1.8 lenses. Granted the 50mm f/1.8 is known as the thrifty fifty. Its quality isn't top notch, but it's fast and pretty sharp for its price. Great value. I'm planning on upgrading to the 50mm f/1.4 which is mucher better quality, but I highly recommend the 50mm f/1.8. The Sigma 30mm f/1.4 is another great alternative, especially for those with tight spaces. If you're looking for a good zoom, the Tamron 28-75mm f/2.8 is a great zoom for the price ($500). A good zoom doesn't come as cheap, as they're more expensive to make - more moving parts.
So in the end, it's obviously up to you whether or not you want the kit lens. I personally would skip it, especially if you plan on that being your only lens, or the only lens you'll have for a while. I feel like it would cause more frustration than anything, especially if you plan on using natural light indoors.
The only kit lens I would consider is the 55-250mm IS. While it is a variable aperture lens, you'll be using this lens primarily outdoors. It has IS (which is a must for longer zooms), and even though it doesn't shoot very wide, on the 250mm end it will still give you a pretty shallow depth of field due to the long focal length. (see DOF calculator: http://www.dofmaster.com/dofjs.html )