Hitwise shows a consistent 2-to-1 advantage in unique site visitors for Obama's official campaign site in a head-to-head comparison, from August through early October -- with the exception of a significant narrowing of that gap around the week of the Republican National Convention.

Comparing the two campaign sites against other popular sites on the Internet tells a similar story. Compete.com ranked both campaign sites in the top 500 Web sites in the United States for September -- with the Obama site significantly more popular at No. 186 than the McCain site at No. 384, even though the latter has made up tremendous ground over the past year.

Similarly, numbers from Compete show the Obama campaign site serving about 64% of the total unique visitors to both campaign sites for the year ending in September. The graph shows that the Obama site has managed to sustain a large early lead built up during the protracted Democratic nomination contest, despite rapid growth by the McCain site as the general election campaign itself intensified over the summer.

Quantcast had rankings similar to Compete's, with the Obama site sitting at #115 with around 7.9 million visitors, compared with the McCain site at No. 272 with around 4.3 million users (this matches with Compete's traffic split as well) . These Quantcast traffic trends also showed a "pinch" at the time of the Republican convention in an otherwise wide and relatively persistent gap. One additional point of interest in the Quantcast data is a noticeable widening of Obama's normal (pre-convention) advantage, starting sometime around the middle of September. Quantcast, at least, appears to show Obama pulling away.

The popular Alexa traffic tracking service tells a very similar tale. The Alexa service shows the McCain campaign site with a traffic rank overall on the Internet of 3,074 while the Obama site is ranked 869 overall. Comparing the two sites' traffic patterns using Alexa shows the same general trend, with the now familiar convention-related pinch and an otherwise sizable gap in Obama's favor. The Alexa data also -- like the Quantcast -- shows a discernable, widening of that gap starting around mid-September.