Link Affordance Test
A great affordance test is to print off web pages in grayscale, give a test user a yellow highlighter and ask them to highlight anything on which they think they could click.
The first thing you will notice is that anything that is underlined will get highlighted. Those words that may or may not be colored but which are not underlined will most likely not look like links to your test user.
Headlines that are not linked might also get highlighted because they are different in size, weight and location to the main content, all possible visual cues to a desperate information seeker. Users may also highlight images that are not linked while overlooking images that are linked based solely on subtle cues like outlining, drop shadows and 3-D effects.