If you build websites for a living. Now is the time to Go Here and download a preview copy of Internet Explorer 8. The important thing is that you do this BEFORE the browser is launched and not AFTER. This will prevent a future incident where your inbox will be filled with complaints from customers.
That being said IE8's standards compliance is much better so problems (if any) will be minor, but it always annoys me when companies use the "It wasn't out so we couldn't test against it" excuse when there was a preview build (specifically for compatibility testing) available months before the official release.