One downside of having an author pic might be that it will be used in preference to the pic (for some) which appears in the SERPS because of Rich Snippets.
For example, say I have created a recipe page for "lamb in cat's pee sauce". At the moment my entry in the SERPS for that recipe (courtesy of Rich Snippets) shows a picture of the cooked result of the recipe.
Would I prefer a picture of my cooked recipe in the SERPS or a picture of me? I vote for the cooked recipe picture. So why would I go for the authorship option?