Basically it serves up your web pages from a data center in your area as if we we're local instead of just one server location for everyone.
Your browser has a user agent string which has some basic identifying information. You can check yours: http://www.useragentstring.com/ Usually bots and crawlers won't have a standard user agent which generates that captcha. The CDN will also look for other attacks and basically filter those out. Snort on your shield will drop those too.
Thanks for the Oz fix.
Think you're right, I see the resumé site is linked from the Nabble home page too. I have (and prefer to keep) popups enabled to open in new tabs, so the alternative I went with was to add super-resume.com to our fancy Web Filter black lists