On a page, I want to display content from four areas, posts and three custom post types, and sort them all by date. The post date is post_date and the cpt dates are meta_value values called, for example, cpt_date1, cpt_date2, and cpt_date3 (containing strings in unix date format).
How do I write arguments for WP_Query to accomplish this?
Any help is appreciated!

post_datevalue for the custom post type as well? It should be the same as the default post type, unless I've missed something about why you would want to declare it as meta value. – Brent Sep 14 '12 at 5:58