Interesting topic, Cai. My brother (personal trainer) and I actually had a long drawn out discussion about this topic recently and I thought I might give you all a summary of the things he said. I don't know if I'll remember everything though so keep that in mind.

Things that affect your metabolism:

Lack of sleep - the less you sleep, the slower your metabolism. The more broken your sleep, the slower your metabolism. Get good quality sleep if you want to stabilise your metabolism.

Yo yo dieting - everytime you 'starve' your body by dieting, your metabolism slows down. Diet often and your metabolism will be truly slow, and you will find it harder and harder to lose weight each time, and will put it back on faster.

Number of children you have - the more kids a woman has, the slower her metabolism is.

Gender - women's metabolism is slower than men's.

How much and how frequently you eat - eating small, frequent meals does increase your metabolism. A small meal is equivelant to an amount equal to or less than the 2/3 of the size of your clenched fist. The meal should consist of 1/4 veg, 1/4 carbs and 1/2 protein.

Amount of muscle you have - the more muscle you have, the higher your metablism. So while aerobic exercise will burn calories, it doesn't increase your metabolism like 20 mins of resistance exercise 3 times a week does.

Your age - the older you are, the slower your metablism. The best way to counteract this is with resistance exercise.

Amount of water you drink - drinking less than 6 to 8 cups of water will impede your body's ability to dispel toxins and excess nutrients. It also causes you to feel hungry (as the body often confuses thirst with hunger)

Thought it might be of interest to some of you. It's lots of small things we can change about the way we live that can help a sluggish metabolism. Anyway, just my contribution to the thread.