Mono 2.0 will mark the time when the class libraries have complete support for the new features in the 2.0 edition of the framework.
Notice that Mono 1.1.x already contains many of the 2.0 features and class libraries, there are just no guarantees that they are complete, you will have to compile and test your application with Mono (using the gmcs compiler instead of mcs).
In addition, an "add-on" to the core of .NET has been released, called ".NET 3.0", but it does not touch the core. It is a set of new APIs and extensions that run on top of a .NET 2.0 installation.
.NET 3.5 is the actual heir to .NET 2.0, and it contains updates to the core libraries (small bits) and new assemblies (like System.Core).