A new report from Net Applications shows iPhone usage to represent 0.40 percent of Web hits, down from a high of 0.48 percent last week. This is up from 0.19 percent in July when the 3G iPhone was first released.

This may not seem like a lot, but consider that this percentage measures Web hits coming from all Internet connected devices — not just mobile. On that measure, there are about 1.4 billion Web-connected devices, only 270,000 of which are iPhones. So essentially the iPhone makes up 0.019 percent of devices but 0.4 percent of Web activity.

There are lots of fairly obvious reasons for this, such as iPhone owners’ propensity to show early adopter/power user behavior. Many of these dynamics were discussed in a past post that compared iPhone data consumption to that of other smartphones and mobile devices.

These reasons also make iPhone users a desirable target demographic as they’re generally young, affluent, tech savvy and fashion forward (see NearbyNow’s thoughts on this). As iPhone penetration increases and follows an adoption curve similar to that of the iPod, it will be more of a mass market device and this level of targeting will be traded in for reach.

How mobile marketing will play out and evolve with the iPhone’s changing hardware and software standards is yet to be seen. We’ll see display ad models develop. But as we’ve argued, Apple’s progress with local search applications (and mobile’s inherent ties to local) will mean that a great deal of ad models that develop will be more location based and directional in nature.