Disclaimer: I am the PM for the #develop project.
After almost two years in development, the #develop team has shipped version 2.0 of its open source integrated development environment (IDE) SharpDevelop2. The new version supports the .sln / .*proj project file formats of Visual Studio 2005, therefore you can open and edit existing projects inside SharpDevelop2. The team however does not view SharpDevelop2 as a competitor for the Express line of products (comparison) from Microsoft, but it aims at software developers that need best of breed tools for their software development process - like unit testing, code coverage, documentation generation and more. In the same vein, version 2.1 will complement those existing features with integrated source code control, code analysis tools as well component testing.
SharpDevelop2 is especially well-suited for developers that chose the Boo language, because SharpDevelop2 offers first-class support for code completion as well as the Windows Forms designer. Aside from this unique selling point there a couple of smaller but nonetheless productivity-enhancing features in version 2.0: code conversion (eg VB.NET to C#, but see for yourself), support for Mono, documentation preview, RegEx compilation und quite a few more.
A lot of the features are owed to the ease of integration and extensibility provided by the addin system found in SharpDevelop2. This addin system can be used by developers in their own application - this being the reason for the rather unconventional license choice for SharpDevelop2: LGPL instead of GPL, which is much more common for development tools such as #develop. Re-use by third parties has been the driving factor to change the license.
Thanks to all the contributors that made SharpDevelop2 a reality, especially the technical lead on the 2.x effort, Daniel Grunwald.