Design Time Compilation in Vs 2008 Sp1

I have been playing around with Vs 2008 sp1 bits and one of the very cool debugging improvements I have noticed is, you don't have to compile the project to see compilation errors. By default C# compiler would put squiggly lines below the code that is causing the problems and when you hover over the squiggly lines it will show the exact error that you would get if you were to compile the project. I think this feature offers a tremendous developer productivity. I cant imagine how many times have I actually compiled the project to see what error the compiler gives me. But now with this feature I will save so much time. All I have to do is hover over the lines that is causing the problem I will get the same error as if I was compiling the project. Hats off to C# team in pulling off this feature. Screen shot below shows this feature in action.