I've just tagged and released mitmproxy 0.5. Everyone should update - this release squelches a few annoying performance killers. You can download it from the project website:

mitmproxy.org

Changelog

• An -n option to start the tools without binding to a proxy port.
• Allow scripts, hooks, sticky cookies etc. to run on flows loaded from save files.
• Regularize command-line options for mitmproxy and mitmdump.
• Add an "SSL exception" to mitmproxy's license to remove possible distribution issues.
• Add a --cert-wait-time option to make mitmproxy pause after a new SSL certificate is generated. This can pave over small discrepancies in system time between the client and server.
• Handle viewing big request and response bodies more elegantly. Only render the first 100k of large documents, and try to avoid running the XML indenter on non-XML data.
• BUGFIX: Make the "revert" keyboard shortcut in mitmproxy work after a flow has been replayed.
• BUGFIX: Repair a problem that sometimes caused SSL connections to consume 100% of CPU.