The power of writing declarative code (versus imperative code) is that the developer focuses more on expressing the “WHAT needs to be done” rather than “HOW it is to be done.” This is important because it leads to many benefits. One of the benefits is that the impedance mismatch that happens between the problem a developer needs to solve, and how he solves it becomes less and less. Currently, expressing solutions in an imperative way does not allow a developer to express the true intent of his code.

The only advantage of a declarative programming model is that the compiler and runtime can be more liberal with the changes it implements in order to make the code as efficient as possible. This is due to the fact that the code is no longer directly tied to the implementation of the underlying algorithm like it is when using imperative code.

the new c# 4.0 will have much improvement on declarative code, so not miss it!