Checked Exceptions

Here is more hand-cuffing from Sun: Checked Exceptions (read here and here).

Why there are checked and unchecked exceptions?
Aren't both equally dangereous for your program?
And why checked? Why do people have wrap and to push an exception up to the point where checking makes a sin?
Is my program more safe if I use Checked Exceptions? Hmmm. I would understand it from a declarative point of view: I tell you, my API Customer, that this function will/ throw an exception,
but how do you handle it is your bussiness, and not the compilers. But eventually you and I will have to write TestCases for your code, and these Specify/Document my API and your code.

Haven't we learn anything from Smalltalk?