The capability to update a page without a visible round-trip to the server is generically referred to as innerbrowsing. Innerbrowsing has the advantages of presenting the user with a seamless and snappy interface to your site, almost as if the page were an application. But it also has significant usability problems.
One major problem is that the state of the page can easily be lost. That is, any changes to the page that are the result of user actions don’t persist the next time the user loads it. This is problematic if the user clicks Reload, if the page has been bookmarked, or if the user wishes to send a link to it to a friend. You can get around many of these problems by storing state information in cookies, but doing so can be tedious, and might not be worth the effort, particularly if the content available at the page changes frequently.
Another significant problem with innerbrowsing is that it modifies the traditional Web browsing paradigm often with troubling consequences. For example, innerbrowsing may appear to break or modify the meaning of the Back button to the end user. In many browsers, depending on how you have implemented your RPCs, clicking the Back button may cycle the sections that were part of the innerbrowsing that may not be desirable. Pages that use innerbrowsing also may be troubling to bookmark in a predictable manner. Consider that the user would expect to bookmark the particular state of the page they were at, but depending on the way innerbrowsing was used, it might not be recordable. Likewise, because navigation has been significantly altered, search engines will generally have problems with innerbrowsing-oriented interfaces, which may or may not be an issue depending on the type of site or application you are building.
Yet despite these and other challenges, innerbrowsing is on the rise, particularly in Web applications. Implemented both using Flash and standard (X)HTML, innerbrowsing interfaces provide a software application–like experience, which, when implemented properly, can be highly usable and satisfactory to users.