Handsomedan: Personally, I have always been a bit of a late bloomer.
I usually upgrade about 6-8 months before the latest model comes out and never really feel like i have missed out at all.
That might change with the next one, but having just leapt into a new iPhone 5 a week ago, I can honestly say it's like putting on comfortable slippers that have been made from a slightly better material (terrible analogy, I know).
I have had an iPhone 3G, 3GS, 4, 4S and now 5 and I have followed this late upgrade pattern all the way. Don't regret it for a moment.
It's all very personal - if a high MP camera, fingerprint recognition and permanent 4WD with traction control are important to you - wait until Sept/Oct for the new one.
If not, pull the trigger.
We pulled the trigger last Friday and got iPhone 5 each for both of us. This was expedited by a very enticing great On Account plan and bonus deal from Vodafone, with nice big phone subsidy.
With new announcement, the phone won't be physically released until at least 3-4 months and being in NZ, it would be quite limited quantity as well... so 5-6 months before the supply be adequately available.