I have this issue and already initiated an exchange. You can find my experience here (aut0maticdan):
https://discussions.apple.com/thread/4034848?start=0&tstart=0
I have a lot of computers and monitors, mostly apple, the only discernible ghosting can be seen on a 2005 23" Cinema Display. None of my ipads, iphones, imacs, macbook pros or macbook airs have ever exhibited much of anything. I still have many of them around and confirmed this.
Even if you compare back to my 2005 Cinema Display, the situation is very different here. That may have some evidence of ghosting after a day of having a terminal up in the same spot. No big deal. I can detect ghosting on my rMBP after 60 seconds of having something over the affected area. If I put the calculator over the spot for five minutes, I can clearly read the buttons/numbers against a dark blue background.
I initiated an exchange a few days ago. I have to wait 3-4 weeks for the exchange, but they let me hang on to the one I have, which is great. In the last few days the problem has become much worse and now covers an area 3x the size it did when I went to the genius bar while also being more sensitive to ghosting.
I'm happy they were so quick to order me up a new one, but if the exchange has anything similar to the problem I am having now, it will be refund time. It is, unfortunately, quite possible this is a wide spread defect which is going mostly unnoticed due to busy backgrounds. Time will tell. Its always a good idea to wait for second gen, if you can.
There is little reason to get too worked up about it. Their support is excellent.