I checked Ticketmaster at 9:15 this morning. Two nights of Madonna at MSG were completely sold out fifteen minutes after tickets went on sale to the general public. Actually it's not surprising - they were probably gone almost instantly. I just checked eBay. Also not surprising - half the stadium is up for sale, and plenty already have new owners. Somewhat surprising - what some people are willing to pay...

A SAMPLE OF ACTUAL COMPLETED EBAY AUCTIONS
Madonna