I dated my best guy friend( we have been friends for 4 years now) but it didn't work out for me. Although it does work out for a lot of people and has the potential to be the greatest relationship. In my experience it was a little awkward because it was hard for us to transition to something more. It didn't work out between us but we are closer for it and he is still one of my best friends. I love him and I couldn't imagine life without him. We where just not right for each other or maybe it wasn't the right timing who knows.
Its only awkward if one turns the other down or isn't certain about becoming or then friends. But other than that those kinds of relationships usually turn out the best because the people all ready have a good understanding of each other.