Wanted to make sure that a comment from Brad Noble, head of Info Arch at Mullen, on a post below didn't get lost in the pageview shuffle. While he's responding to a post on brand irrelevance, his remark is also more evidence for another point made below: planners need to engage with the discipline and tools of Info Arch if they want to understand consumer experience online.
Responding to the usability work done by Jakob Nielsen here (definitely check it out, the eye-tracking heatmaps are worth the visit alone) Brad points out how strongly we've be conditioned to ignore what he calls "distractions" (e.g. advertising) online and to respond strongly to what appear to be functional elements.
As Nielsen remarks, among a bunch of other well-articulated points, "Users almost never look at anything that looks like an advertisement, whether or not it is an ad." Now that's irrelevant.