I havent even thought about upgrading to a 4S but will be upgrading to the 5 when it's released. Whilst android phones can seem to offer more, for someone like me with several macs, ipad, iphone, apple tv etc any other phone is simply not an option I would consider. At the end of the day its quite a personal choice how our phone fits in with our lifestyle.
For me being able to pick up any device at home and instantly have access to all my music, videos etc on my TV or any speakers in the house always brings a smile to my face. Others may not see that as anything other than a gimmick, again personal choice!