"Ironically, removing page refreshes can make for a refreshingly interactive experience. However, eliminating the refresh doesn't come for free. When is it worth the investment?
Amazon's Helpful Reviews
Out of the 5,424 reviews listed on Amazon.com for J.K. Rowling's Harry Potter and the Sorcerer's Stone, it's a July, 2002 review by Victoria Tarrani that the site displays first. That's because 443 people have indicated this was a "helpful" review, out of the 533 who shared any opinion on the matter. Amazon bubbles the reviews voted most helpful to the top of the list, to prevent them from becoming buried by more recent reviews that are less useful.
A simple question at the bottom of each review asks the reader if they've found the review to be helpful. Those that feel inclined to respond can choose between two buttons, simply labeled Yes and No. While Amazon has sold millions of copies of this book since 2002, very few have shared their opinion of Ms. Tarrani's review. However, the few that did have provided a valuable service to future Harry Potter shoppers.
The interesting part of the helpful buttons is they don't refresh the page. Instead, upon pressing the button, a message appears, first informing the reader their feedback was being saved, then thanking them for their vote.
There are other ways Amazon could've implemented this same functionality. They could have, for example, stayed with the traditional button behavior, building the question into an HTML form tag. Pressing the button would do practically the same thing as the current Ajax behavior, except a new page would be returned.
From an implementation standpoint, the communication with the server is almost identical with this method. From the user's standpoint, however, it would be dramatically different. The user couldn't continue interacting with the page, until the new page was loaded. Returning the user to the same point in the page would be difficult, creating a jarring effect. (Anchor tags could get the browser to the same general neighborhood, but the page would likely shift from its original configuration.)
The designers at Amazon wanted to make the action subtle. Another option would've been to use radio buttons for each review. Clicking the radio button to indicate Yes or No wouldn't invoke a page refresh. However, to register the vote, users would have to remember to press a submit button. It's likely that users might forget to do this, thereby neglecting to get their votes registered, and defeating the purpose of the function.
For Amazon, Ajax is the right way to implement this functionality. However, deciding when to use Ajax to eliminate a page refresh is not always easy.
At Netflix, Ajax Pushes to the Top (Sometimes)
The designers for Netflix.com are big fans of using Ajax to eliminate page refreshes, having been a pioneer with the technique from the early days. (They were one of the first, using it to register how many stars their subscribers rated each movie.)
Interestingly, they don't use it for everything. One place where this jumps out is in the movie queue. Subscribers add DVDs they'd like to watch to the queue and use it to manage the order they'll receive the discs.
The queue functionality offers three ways to change the order of the list. In the early versions, subscribers entered a number into a type-in field next to the movie and pressed an update button. Putting a '2' in the third movie would move it to the second position on the list.
Because the most common subscriber action was to choose the next movie to watch, the team added a "TOP" button to move the disc to the top of the list. In the most recent version, users can also drag the movie into the new position.
It's interesting that the original number-and-button operation still results in a page refresh, while the new operations don't. Similarly, on the same page, rating a movie doesn't have a refresh, while deleting a movie from the list does.
This isn't by accident -- the designers have made these choices deliberately." (Continued via UIE, Jared Spool) [Usability Resources]