One of the reasons I've decided to move is that I do a fair bit of my contracting in APAC, something like 20 weeks a year is already spent in China, Australia and India.

When I do eventually get a visa and I move down, I'll continue to do the same thing with the same clients, so I will spend quite a considerable portion of each year outside of Australia. Each trip is usually short (2 weeks at most) although on the odd occasion I have been known to go off for 8 - 9 weeks at a time.

What impact will this have on me, for instance will I be able to still seek citizenship after 4 years, or will each period of absence count against me?

Yes, each period of absence may (and in your case almost certainly will) delay the point where you are eligible for citizenship. You will need to fix yourself a RRV in order to be able to travel.
NJ

Thanks, NJ

You confirmed what I suspected. As long as I won'thave an issue getting an RRV, I don't suppose have to worry.