We really can crawl XKCD in 7 seconds.  Mention Python 3.3 and Windows.
Ignore popular temporary files.
Ignore @*, not just @.
Separate main() and library classes. Rename library module crawling.py.
Oops, *~ is already being ignored by the root .gitignore file.
Simplify pool pruning.
Avoid using internal attributes -- there are official APIs for these now.
Switch to using the logging module.
Quick Makefile with commands I run all the time.
Fix logging lines I screwed up.
Squeeze a few lines out of send_request().
Move reporting subsystem into a separate file.