A recent attempt at converting a 1.8GB database from MyISAM to InnoDB ran past 5 hours which triggered this quest to look for tweaks to improve the conversion speed. I was able to bring down the conversion time from 5+ hours to a mere 8 minutes.
You may need to play with the settings above to suite your environment.
Once this is done, restart mysql with the following command to disable InnoDB Double Write Buffer. You want to do this before start converting the database:
Once your done restart normally: