Let’s start to say that, while getting a good reference from a well respected supervisor would surely help in getting a job, it is important to notice that I used the word *help*, not the word *guarantee*. In addition, we are talking about *a job*, not a whole career, and the original question seems concerned on the long-term benefits of working for or being supervised by someone with a big name.
To give an articulate answer to this question I hope you do not mind if I take a slightly roundabout approach. Many years ago, as a young postgraduate student I attended an informal meeting where two postdocs gave us young whippersnappers the lowdown on how things work in science. We were told, in no uncertain terms, that to have a successful academic career it is incredibly important to find someone (whether your supervisor or someone you work for or have worked with) who is willing to take a very active role in helping you getting positions and funding. Someone who is very active, we were told, means much more than writing a polite reference for a job, it means singing your praise loud and clear to all sundry, badgering people to consider you for positions and your projects for funding, and so on. Obviously, the better known and respected your number one fan is, the greater the benefit. I admit that we were taken aback by such blunt admonition, the implied cynicism of it. Surely our intellect and passion would be enough to make perfect strangers notice us (I would not be able to say whether we were too innocent or too conceited)! Over the years tough I have witnessed first hand that this advice (or warning, if you like) is true: having a very established colleague who believes in you and is willing to invest in your career gives a huge advantage. You might be the very best thing after sliced bread, but having another person actively going around saying so is a different ball game altogether. Obviously, if you *are* the best thing after sliced bread sooner or later people will notice, and doors will open. Having a strong supporter will help making the doors open sooner rather than later though.
This observation brings me back to the original question: would having a famous and respected supervisor help your career prospects? Well, if you have an excellent working relationship with your supervisor, and you prove to be someone with great potential, and you prove yourself, your big name supervisor might be happy to help you along the way, putting much more effort than just writing a nice positive letter of references. But as you can see most of the previous statement is based on caveats, hence my first short answer ‘it depends’. I understand the concern of those who are worried about their long-term prospects, and whether we like it or not, taking such long-term view is becoming more and more important for a fledgling academic. At the same time I would suggest that a student is far more likely to be noticed for the ambition to have some intellectual and scientific achievement to their name, and not just for the design to go up the food chain of academic ranks. Thus, if what you want is your scientific and intellectual progress, and to make a valuable contribution to your chosen field of work, then my suggestion is that the only reasonable thing to do is to choose the supervisor who is most likely to help and support you achieve these goals. How big the name of that person is just a side issue. And do not discount the fact that it is also possible that along the way you will find a mentor in someone that is not your PhD supervisor! This is why it is crucial to network and share your work so that others also sit up and take note.