Regardless of what OS you have running on Apple hardware, the build quality and aesthetics of a Macbook Pro beats anything available from manufacturers like Dell, HP, Lenovo, IBM, etc.
OS X provides a good trade-off between developer friendliness (because it's unix) and usability when you don't want to mess around with stuff. However, I have on more than one occasion read about developers who are pushing the limit of their development productivity get fed up with OS X and install Linux as well for when they are developing.
Thinkpads aren't nearly as sleek looking, but they are IMO much easier to work on, and no integrated battery, and on some (T400 in my case) 100% hardware support for Debian/Ubuntu/CENTOS out of the box.
OS X provides a good trade-off between developer friendliness (because it's unix) and usability when you don't want to mess around with stuff. However, I have on more than one occasion read about developers who are pushing the limit of their development productivity get fed up with OS X and install Linux as well for when they are developing.