I've been using WP Super Cache now for months, and it's been working great. Recently, I noticed that the front page of my blog is no longer caching. Interior post and category pages cache just fine, just the main index (and page 2, 3, 4 and so on).
Since the front page of the site gets the most traffic, it is the page that I definitely wanted cached. I thought I'd check to make sure index.php was added to the accepted files, but it doesn't seem to matter.