Orchard 1.6 RC was released last night and I encourage you to spend a few hours testing it using fresh installations and upgrades of your Orchard CMS Websites. This is a fairly critical version in that it runs on .NET Framework 4.5 and leverages ASP.NET MVC 4, ASP.NET Web API, MySQL and other technologies. I know a lot of Orchard Developers prefer to wait until 1.6 is released before downloading it, but it's more helpful to download and test the RC. Think of it as a RELEASE. We want to catch any bugs before Orchard 1.6 is released as opposed to coming out with a quick Orchard 1.6.1 maintenance release.