I don’t know when they released it, but it has a huge amount of fixes and improvements.

The Release notes page says it all.

Edit:

Apparently they did it yesterday.

Today, we’re excited to announce the release of ReSharper 4.1! This minor version is highlighted by:

* Support for Microsoft Visual Studio 2008 SP1
* Enhanced ASP.NET experience
* Improved performance and usability: quicker solution load, optimized Unit Test Explorer behavior, and more
* New minor features, including name editing in code generation UI, generating backing fields for implemented interface properties, highlighting usages of XML tags and attributes
* Stability improvements and bug fixes

See Release Notes for details on bug fixes, cosmetics, new features, resolved performance and usability problems.