Is there a preference?
I'm sure this has been asked thousands of times.

I'm thinking of leaving in May 2009.

Would like to hit:

South America
Africa (Capetown <-> Nairobi, doing overland + Kili climb, either direction is fine with me) + Egypt.
India (although given latest events, just dropped in priority)
Asia (Thailand, Vietnam, fly around on tiger airlines...)
Aus+NZ. Hang out here a bit if I can.

Would prolly want to hit the shoulder season as many places as I could to save $$$.

Ideas?

there's an interesting question!! I never even thought of whether there was a "better" way to do it.

Personally, I'm going East-ward, starting in a month!! Eek!

In terms of direction, the effects of jet lag are supposedly decreased if you head west. The logic being that it's easier to stay up later than usual rather than always waking up earlier. I think that depends somewhat on whether you are an early bird or a night owl. Early riser types might want to head east. Night owl types might have an easier time going west. It also depends on how fast you are traveling and whether you are trying to follow seasons and such. Jet lag isn't much of a factor if you're mostly going overland.

You might want to research your specific destinations and figure out what timing makes the most sense for each one. Then try to string them together into a route. You may discover that you'll need to jump around a bit or stay longer in certain places.

I went west, no reason really. I would just say go the direction that you get the cheapest flights to the destinations you really want to go to first. You might end up cutting stuff out at the end for various reasons.

I am going west, partly because I'm a night owl so I won't mind staying up late (but know how much I hate waking up earlier!) and partly because the seasons work out much better at my destinations that way.