mashadar - I always write mine. I'm a very kinesthetic learner. And I have ADD. There's a LOT of stuff running through my head all day everyday.
In school, writing and re-writing notes helped me to focus and to anchor the facts more firmly in my mind. Something about the direct physical connection traveling from the paper to the pen, through my fingers, up my arm, and into my brain helped make things stick.
I find the same to be true of writing my intentions. I am able to state my intentions more clearly and maintain my focus. Plus the action of writing forces me to state my intention as I truly desire it to be.
I use a bound notebook of paper with a "good hand" and a smoothly flowing pen. I like the way it feels and the physical action of forming and reading the words helps to make the intention real.