I paid invoice OTD on my Black/Black M6 w/ 17s two weeks ago. Not a super deal, but it was a Nov '05 build date (so no strut worries) and one of only three black/black M6's left in a 100mi radius...so I went ahead and pulled the trigger. Since it was in the town where my gf lives, I had been watching it for quite some time...and knew that 90% of it's lot time was in a showroom. The conquest rebate and all of my (old) GM card points made it a better deal.
I hate I missed the 72-hour sale, but I got the exact car I wanted at a price I could handle, so no regrets here! If GM treats the GTO anything like the 2002 f-bodies, there will be plenty of A4's in common colors on dealer lots for quite some time. In fact, the first GTO I ever saw in person was sitting next to one of those "end of the line" Trans Ams. For some reason GM seems to like letting outgoing vehicles trickle off lots without incentives.
If you want a specific color combo or an M6, you might want to be a little quicker to buy. If you're more flexible regarding color and transmission, you could always wait it out and see what type of sale happens after 9/5.
DC
(Edit: Right now financing options are 12, 24, 36mo for 0%, 48 for 2.90%, 60 for 3.90%, and 72 for 4.90%...if you don't finance, you get $1000 cash back)