There are a few very inexpensive digital cameras on the market that use plastic lenses. Most digital cameras use good quality optical glass. The best of these, and most expensive, use aspherical glass lenses. Aspherical lenses are, as you might guess, not round. It seems that a perfectly round lens can produce a slight distortion to the image.
Aspherical lenses can produce better pictures by reducing the distortion.
Optical zoom is a very important feature on a digital camera. Zoom lets you adjust how close or far your subject appears in your picture. Optical zoom means that your camera actually moves it's lens in and out to optically change the image. The higher the optical zoom the better. Digital zoom does not move the image closer or farther optically.