I am going to be the voice of dissent here having suffer plantar fascitis all my life I have tried everything or pretty much everything that has stated above in this forum with no avail. I even have gone to a sports medicine podiatrist prior to a marathon and he told me pretty much what advised had been stated above.
One credit that I do give him for getting the pain under control prior to a marathon that I had and resting of my right foot was the use of the Straussburg sock. I used this in the evenings while resting or watching TV prior to bed which helped tremendously at night, but most important in the morning prior to waking up the pain started to subside, but not entirely gone away.
With that being said, I am not saying this will work for you, but for me it did. I still use insert for work, but have gradually changed to barefoot vibrams running or minimal arch support for running shoes. I know it sounds absolutely CRAZY because we have been taught or inoculated by the market media to believe that support or additional cushioning of the shoe was the most important to prevent foot injuries. However, the main stream running shoe did not really got is real innovation since the 1970's with Nike coming on board first, prior to that most of our running shoes were flat, and yet we have not see the amount of injuries as we have today. So, I started running with the vibrams and at home using a flat loafer with no support, its been a couple of months and I do not have plantar fascitis pain anymore, which for the first time in so many years is great and awesome.
Just wanted to point another alternative, the best option is to read the other side of the argument to see if its an option.