Re: anything but python
I wish I could upvote you a million times. Significant whitespace has to go down in history as one of the dumbest decisions ever (along with the GIL).
The reason is simple. Your code becomes nightmarishly difficult to refactor. Refactoring is one of the most important tasks in large scale software development since it allows your design to develop with the changing use-cases. But when you have to be ridiculously careful about making sure that things end up at the correct indent level it becomes a nightmare problem. The number of times I've fixed someones bug where they accidentally changes the indentation of the last line of a loop or similar.
Personally, I would have had a terminating token for the end of functions/loops, but made it a syntax error to have invalid indentation. That way after a refactor you can use your editor/IDE to fix the indentation.
I have a few other Python gripes - one of the biggest being the absence of a perl-like use strict type construct. If you have ever had to debug a problem where a thread dies due to a syntax error in a little used code path, you will totally get my annoyance.
Incidentally, and without wishing to start a flame war, my favourite language is C++, and I think Julia is the one to watch for.