(2) Was the pain worth it, or would you prefer we'd spent more time on being more backwards compatible?
fwiw, I think it would be a really good idea to decouple (large portions of) the standard library from the interpreter core, and keep the same code base running on multiple versions.
if not else, it would force the core developers to "share the pain" ;-)
I thought Gordon was saying that most of the pain was to fix code that accidentally worked in 1.5.2 but broke in 2.0. Whether or not you fix that in a backwards-compatible way, we've all shared that pain already.
Other than sharing the pain, I don't see much of an advantage.
--Guido van Rossum (home page: http://www.python.org/~guido/)