Although available for download by subscribers the last few days, the second beta release of .Net 4 is now available to everyone. You will see a number of new WCF features changed or moved around since the first beta release, but what you see now is almost everything planned for .Net 4.
If you're planning to test .Net 4 for compatibility, then I highly recommend doing that as soon as possible using this beta, preferably in the next few weeks. It's virtually impossible to address any but the most severe issues once the release date gets close. Waiting to test can delay getting your feedback addressed for years until the next service pack or release comes out. Use the Connect link to the right as the best way to make sure any issues you find get recorded.
Here are the resources available.
There's one significant known issue that affects WCF services hosted in IIS.
ASP.NET and WCF applications might fail to start in IIS 7 Integrated mode
If new configuration sections are added to the application web configuration file of an ASP.NET or WCF application, the application will fail to start when it is running in IIS 7 Integrated mode. For example, if a
There are several other minor known issues with IIS and ASP.NET so check the readme if you're having problems with web hosted services after upgrading.