I had an iPhone 2G and absolutely fell in love with Apple at that point. I then upgraded to a 3GS and that was a big leap in tech from the original, especially having 3G. It was at this point I made the mistake of trying out Android because I liked what I was seeing, so I sold my 3GS and got myself an HTC Desire. I had it roughly 4 or 5 months before I realised the error in my ways and got myself an iPhone 4, haha.
It would take quite a leap for me to upgrade to the iPhone 5, so I might only upgrade again in 2012 when the 6 comes out.