I am a Realtor in Marin. According to my husband, who commutes to Pleasant Hills every so often (yes, I just checked with the expert here), the commute from Novato (the north most town in Marin) to Pleasant hill is about 45 minutes.
If you live in San Rafale, the commute time will be much shorter because you will miss the mess where the lanes change from 4 lanes to 3 lanes and the other construction mess where they are widening 101 from 3 lanes to 4 lanes.
If you live in Sourther Marin, your commute will be against traffic going up north to Richmond (580) bridge as well going south back to Mari; so the commute time should be less.
You have to use the Richmond Bridge 580 if you are commuting from Marin to Pleasant Hill.
You did not mention other than wanting to live in Marin, what requirements (commute, number of bedrooms/bathrooms, price range, shools, parks and recreaion, outdoor activity, view, etc that you want to find out..
With a little more details, I will be ablet to find and email some properties for you and then we can see how far and how long a comute it might be for you - if you are not worried about the schools, I have a couple of great places where my mother-in-law lives that are very close to 580 and will be great for commute.
Hope this helps.