Nancy Silverton wrote an article in the May 26, 2011 edition of the Los Angeles Times about focaccia. This is part of a series of articles in the LA Times food section providing "Master Class" with some renowned chefs. You can read the article here:
As most readers of this forum are probably aware, Nancy Silverton is the founder of La Brea Bakery and Mozza Pizzeria in Los Angeles. There are very few people who know more about bread and pizza than she does. She emphasizes that the key to a good focaccia is a very wet dough and a long fermentation time. She also says that using a sourdough starter is an ideal way to achieve the light, airy structure required for a good focaccia, but recognizes that most people don't want to go through the hassle of creating a starter, so she offers a poolish pre-ferment to get similar results. She also advocates using a bit of rye flour in the recipe, something I have done sometimes with my pizza recipes (just a bit to help with flavor development). She also advises to make the focaccia in a circular rather than rectangular pan.
Anyway, be sure to read the article since it has some good tips and its not often that you get instruction from a true bread and pizza guru.