In 2001 the Software Usability Research Laboratory (SURL) at Wichita State University carried out a study to determine where users expected to find certain elements on individual web pages. This included search, back to home links etc.
SURL have now followed up this study with another to assess how much the mental model people use when looking at websites has changed. Not surprisingly, they found that the model people used was very similar. Changes in technology had led to some changes in the model but overall there was a large degree of similarity between the results.
Some argue that 'Web 2.0' applications have had the biggest influence on change on the web for a long time. It would be interesting to see this study repeated in a year or two to see if Web 2.0 is really as seismic a shift as some are saying.