dstiles - 8:40 pm on Jul 9, 2011 (gmt 0)
When google analytics first came out I noticed a huge delay on page-load on any site I visited that containined it. As a result, I never added GA on any of my sites and blocked it through my browser controls for any site I loaded. Result: faster page load on GA sites.
In the USA the slow-down for google-based code may not appear too high, but the rest of the world will certainly notice it.
Own-site-based file requests have already determined the domain look-up and source IP so code access will be quick. Looking up a third-party site takes more lookups - several if any of them fail due to a DNS problem.
Internet speed may be high. It is not instantaneous.