Q: How do you get a guitarist to stop playing?
A: Put sheet music in front of him!

Great thread. Good to see all the viewpoints. I'm classically trained so know how to read music easily but when I compose I do it all in the box and don't write it out (though every once in a while will refer to the staff view). My husband had no good music classes growing up so can't read music but through the years he's learning slowly but surely. Another co-writer knows how to read music but also made up his own notation system in grade school before he learned proper notation. So he'd prefer to use his way of writing things, but he has an amazing ear. We each bring something different to the table. It's great when one of us needs help with something we get each other's perspective since we're all coming from different backgrounds.
We've also recorded tons of bands with varying degrees of reading. Some people come in and don't even know what chords they're playing, just what frets their fingers belong on. But those are sometimes the best songwriters, especially for simple stuff. But can become troublesome when it's Band: "Go back to that part where I do that riff that changes and the drummer is going blicketa blicketa" Me: "You mean the verse?" Oh the stories I could tell....
Theresa