When you `work for’ someone, you are his employee; you have been hired by him to do a job. This doesn’t necessarily mean that this individual knows you personally; and chances are you may not be working along with him. Lots of people work for the Prime Minister; it doesn’t mean that Dr. Manmohan Singh knows everyone personally.
How would you like to work for Ambani?
When you `work with’ someone, you work along with the person. He may or may not be your boss. In this case, since the two of you work side by side, you see him on a regular basis and know him personally.
For my PhD, I would like to work with Prof. Nagalakshmi.
Source: “The Hindu” – Know Your English Column – Feb 26, 2008