The fact that people tend to ignore big, flashy, and colourful banners at the top of web pages suggest that screaming out loud doesn't guaranty that something will be noticed.
According to Don Norman, this has to do with conventions. People guide their search using previous knowledge about websites and direct their attention directly to the location most likely to contain information of interest, such as lists of blue underlined links.
Don's moral: "...if you want something to be salient, follow conventions. Violate the conceptual model, even if the violation seems perfectly sensible, and you are apt to discover that readers miss critical information."
- The article Banner Blindness, Human Cognition and Web Design
- November 22, 2004
See also: Visual design (13) Web page design (23) Tips and guidelines (63)