W3 is a great plugin. A must have on any WP install.
I believe I've run into a bug.
W3 automatically creates *.gzip files that it uploads to CloudFront it seems. It then uses these *.gzip files instead of the original files. E.g. styles.css is replaced with styles.css.gzip. A great idea, although I'd love an option to turn it off.
The problem arises when you need to purge the file. It seems the W3 purge tool does not let you purge the 'shadow' *.gzip file. So if I specify styles.css.gzip I get an error. It at least hasn't worked yet for me. it may be because styles.css.gzip doesn't actually exist on the filesystem (?), just on S3 and CloudFront.
But anyway purging styles.css using the purge tool results in the files being in an inconsistent state. S3 will have the new style.css.gzip edits, so will the local WP install, but CloudFront will have the stale style.css.gzip version for up to 24 hours.
What should happen? W3 should purge the shadow *.gzip files when the original file is purged. Or at least present that option to the user when purging.
My current work around has been to find a third-party Cloudfront Purge tool and then purge the *.gzip files directly myself.