Ironically, Google Pagespeed tells us this about zoompf.com:
High priority
Compressing the following resources with gzip could reduce their transfer size by 235.5KiB (72% reduction).
Compressing http://zoompf.com/js/jquery-ui.min.js could save 142.7KiB (74% reduction).
Compressing http://zoompf.com/js/jquery.min.js could save 62.5KiB (66% reduction).
Compressing http://zoompf.com/wp-content/themes/NewZoompf/style.css could save 24.9KiB (77% reduction).
Compressing http://zoompf.com/js/animations.js could save 4.0KiB (75% reduction).
Compressing http://zoompf.com/.../wp-page-numbers.css could save 1.4KiB (73% reduction).
Medium Priority The following cacheable resources have a short freshness lifetime. Specify an expiration at least one week in the future for the following resources:
http://zoompf.com/images/background_pages.png (expiration not specified)
http://zoompf.com/images/clipboard.png (expiration not specified)
http://zoompf.com/images/handles.png (expiration not specified)
http://zoompf.com/images/pages.png (expiration not specified)
http://zoompf.com/images/report.png (expiration not specified)
http://zoompf.com/images/streak.png (expiration not specified)
http://zoompf.com/js/animations.js (expiration not specified)
http://zoompf.com/js/jquery-ui.min.js (expiration not specified)
http://zoompf.com/js/jquery.min.js (expiration not specified)
http://zoompf.com/.../wp-page-numbers.css (expiration not specified)
http://zoompf.com/wp-content/themes/NewZoompf/style.css (expiration not specified)
http://zoompf.com/.../freedownload.jpg (expiration not specified)
http://zoompf.com/.../freeperformancescan.jpg (expiration not specified)
http://zoompf.com/.../logo-disrupt.jpg (expiration not specified)
http://zoompf.com/.../logo-virgin-america.png (expiration not specified)
http://zoompf.com/.../social-icons-32.png (expiration not specified)
http://zoompf.com/.../video-icon.png (expiration not specified)
They basically don't follow their own advice. Credibility -> toilet.