I love walking. When we moved to the Boston area suddenly I was walking instead of driving and I definitely lost weight just from that. If you walk briskly, you can get an aerobic effect, and if you're always running late like I am, you can definitely get your heart rate up there! If I've been in a sedentary slump, I can tell that I've lost aerobic capacity because I'll be winded when I begin walking again.
We tend to go on vacations where we walk a TON, and even with the rich food I eat I usually come home looking leaner. A few years ago I was at my leanest for me as an adult, and although initially it was Turbo Jam and Lauren Brooks that worked for me, I was walking a lot too. When I stopped formally working out for several months, I continued to lose weight until deep winter hit and I wasn't walking much at all.
This thread is reminding me that I need to walk more!