Today (7-Jun-2010) at Information Week in New York, Microsoft announced the general availability of Expression Studio 4 which includes upgraded versions of Expression Blend (including Sketchflow), Encoder, Web (including SuperPreview) and Design.
You can find out the details of each product and download a trial at http://www.microsoft.com/expression right now.
With this release comes a free Upgrade for licensed version 3 (Studio or Web) users! All you need to do is install the trial version of v4 on top of your licensed version of Expression Studio 3 or Expression Web 3 and the installer will find your license and upgrade it to the full v4 product with no expiration. This applies to customers who received their software through retail channels or electronic software download direct. For customers who have broader license agreements (i.e., MSDN, WebsiteSpark, BizSpark) you should install the product using the software provided from your program site.
For more info: