When I had my Vibrant I felt like I absolutely needed a case because the device was so light & thin. I had my MyTouch 4G naked for quite awhile, but found a great deal on an Epik TPU case on ebay, so now that's what I use.
Screen protectors, however, annoy me. It sucks, too, because now I have a shallow scratch on my screen .
I hate cases, they over-bulk your device and make it less convenient to do the ever necessary battery pull, and the concept of providing protection is only true to a degree that is immeasurable, which means worthless!