Carnations are a sturdy inexpensive flower that can be used in many different ways and are easy for a do it yourselfer to use to create create great centerpieces. They come in a wide variety of colors, both natural and un-natural depending on the type of event you are having or color theme you are using. They best way to use carnations is to use groupings of the same color it adds more impact and fullness, otherwise if you mix the colors, it will look low-budget.
Look how fabulous they look all grouped together to create carnation topiary balls. This definitely doesn't look low-budget.
Carnations lend themselves well to creating shapes, look how fabulous they look adorning a monogram or below they have been turned into a cake shape, complete with a pedastal, very elegant look for the simple carnation.
If you are going to attempt to create some carnation centerpieces for your next event keep in mind that when going for the round look you have to pay very close attention that all the flowers maintain the same height or dimension otherwise your ball won't look much like a ball. Stick with the more simpler designs and it will definitely make your attempt easier and much more appealing.