Craigslist - Although craigslist benefits from the familiar newspaper page model, it fails to extend its search capability beyond that of the local city and fails to take full advantage of the portability of digital information.
Expedia.com - When Expedia returns a results list of matching flights it offers the following categories displayed as radio buttons:
Clicking on a radio button sorts the list by its corresponding label. Once again the principal of affordance is violated, in that when a user clicks on a radio button no system response is normally expected other than the option itself being "selected". Typically this choice would then be followed by a "Go" or "Submit" button at the end of the form.
In the case at hand, radio button labels have also been underlined and thus appear as links. The expected system response to clicking on a link is that the user will be taken to a new page. This appears to be an earnest attempt by the designers to alert the user that SOMETHING is going to happen when a button is clicked.
Why is this violation of affordance unsuccessful compared to the previous example of initiating the pop-up calendar from a text box? Because in the previous example there was a net gain of a mouse-click. In the radio button example there is no net gain here, and other more "affordable" alternatives exist. One such example would be to use labeled "pushbuttons" that show a selected and unselected state. When a pushbutton appears to be depressed the list would be sorted by its label. When the user clicks on another pushbutton, the first button springs up and the newly-selected button appears to be selected. One reason Expedia may have avoided this solution is to decrease the use of images which would cause a longer page load time. Perhaps there could be a hybrid solution, using form elements rather than graphics, yet retaining the "selected" and "unselected" appearance.
Another improvement area for Expedia occurs during the otherwise highly-usable "Save as Itinerary" function. This feature allows a user to save previously selected searches, and to recall the results later. Due to the dynamic nature of flight and hotel pricing however, the prices indicated in the saved search results may no longer be valid when accessed at a later date. Expedia does not offer a way of checking current price validity. Instead it uses a link that says simply "Book now to guarantee price and availability." I was too fearful of actually incurring charges that I could not bring myself to further pursue this user path. Better would be for Expedia to use the principal of error prevention and offer the option to "Check whether price is still valid. This will NOT book your flight."
A full analysis of Pandora including suggested improvements can be found here.