Andrew Jorgensen has announced that the 2.8 preview of Mono is available. This is the first early version of what will become Mono 3.0, the next long term supported version of Mono (2.4.x and later 2.6.7 were the last versions of Mono to be supported in this fashion).
New in this release is the improved generational compacting garbage collector, SGen which vastly increases performance.
Support for a high performance LLVM backend which trades off startup time and memory consumption for raw performance which is useful for computationally heavy applications such as financial and scientific operations.
Additional performance improvements have also been made to the Mono core.
Finally Mono 2.8 ships with full support for C# 4.0 (Learn more about C# 4.0 in this presentation by C#’s father, and fellow Dane, Anders Hejlsberg), Parallel Extensions and LINQ to SQL.
With 2.8 comes bundled System.Dynamic, Managed Extensibility Framework, ASP.NET MVC 2 and System.Data.Services.Client (OData client framework), all code open sourced by Microsoft under OSI approved licenses. Meaning Microsoft is now, some what indirectly, a contributor to Mono.
For the full release notes go here.