Exceptions in mainstream languages have a fatal flaw: they unconditionally unwind the stack when thrown. This sacrifices flexibility and makes it unnecessarily difficult to save state or take action at the point of the throw. Of all languages I've ever seen, only Common Lisp really does this right by separating out the concept of signaling a condition and of handling it.

I don't want to get into the details here, but Kent Pitman wrote a great paper on the subject: http://www.nhplace.com/kent/Papers/Condition-Handling-2001.h...