The exception is when you're on cold ground or snow. Then your feet are apt to get cold. But I've used "shorty" pads a lot, and they work fine. In some cases, I've carried a lightweight, foam butt pad, which I stick under my feet at night. The wider pads are designed for car camping or other applications where weight matters less than comfort. They're great for restless sleepers, or when you're using a rectangular sleeping bag.
The market leader in pads has for years been the Therm-a-Rest from Cascade Designs, a self-inflating pad with a foam core for insulation. The Classic Standard ($65, or $50 for the three-quarter length; www.cascadedesigns.com) remains the pad against which all others are judged; it's a full-length pad that offers good insulation, plenty of comfort, and durability. The Therm-a-Rest Ultralite 3/4 ($60) weighs about one-third less than its Standard cousin, yet still offers good comfort. A good lightweight full-length pad, meanwhile, is the Slumberjack Denali Cross-Core Long ($65; www.slumberjack.com), which weighs just over two pounds. Any of these pads will give you years of good service and sweet dreams.