I noticed an interesting thing in reviewing the winners list.
I was buying some Final Fantasy soundtracks anyway, and they seem perfect to increase your chances of winning (lots of songs for low price), so I figured I'd give it a shot. I aimed for one of the 100,000 marks, then for the half-bil, based on repeatedly reloading the Apple.com counter (which appeared to "re-synch" to reality every minute or two if you reloaded it).
The interesting thing (other than the song count suddenly spiking from 498,199,500 to 499,201,000, probably on account of the buying spree) was that when I compared my reasonably well-timed purchases to the times given on the winner list on Apple's site, the actual winners were off by a few minutes. It's obviously possible that it's just a clock thing, but it looks like the counter you see and/or when your purchase gets "counted" is off by a few thousand from whatever count they use to calculate winners.
So, basically, timing carefully wasn't going to do you a lot of good.
(Unrelated note: having Final Fantasy soundtracks on iTMS are awesome, but the FF VIII soundtrack and it's orchestral companion don't include Eyes On You by Faye Wong for some reason, causing me to grow very angry for a brief period after not winning anything, either.)