According to the San Francisco Chronicle, Marsha Garces Williams filed for divorce last Friday citing the always popular irreconcilable differences. I think that anyone who is married to Robin Williams is going to have differences, and to have survived them as long as she has, shows that the woman has incredible patience and stamina, not to mention a love for all things hairy.
According to rumor and rampant speculation, the couple have not been living together for many months, and that this has been in the works for quite sometime. I think as the story evolves there will be lots more to come out which should be incredibly interesting.