A9 has a comprehensive, all-encompassing interface to their search engine. My friends seem to feel it is clunky, but I think the interface provides more value than the clutter takes away.
Yes, it presents a lot of information, but it does a good job of structuring it. It categorizes the results in ways a lay searcher is most likely to be interested in. For someone doing research on a topic, the static set of tabs may not be the categorization he wanted, but 90% of searchers will like this interface. People will also like not having to do multiple round-trips to do other types of searches even if the overall search is slower, because the results become visible incrementally. A9 will also increase the usage of specialized searches because of this interface.
The fact that A9 maintains personal search history is pretty cool. It often happens to me that I remember searching for an Austrian painter, but I don’t recall enough text about him to be able to replicate the search. Reference search is a good idea which the other SEs do not seem to have.
The killer is, of course, book search. Google Print has also done a good job in this area, but for A9/Amazon it drives direct revenue... and with much higher ratios than sponsored results do for other SEs. A9 bolds the entire book titles (along with bylines and subtitles), which are much longer than web page titles; on a results pages, the books will attract most of the user’s attention after images. You can see the strategy at work in movies results - since those go to IMDB they are not bolded. Even worse, they are in smaller font than the other results. Obviously, A9 will do tests to see how much users will mind them going directly to Amazon, and THEN movie results will be bolded too.
The diary feature is good because when people start making notes about sites and about their history, and mail those notes to each other and comment on each other’s notes, and maybe have the entire thing automatically published as a blog, the SE will get very sticky. However, I suspect, not many people will actually use it beyond a point, unless A9 come up with a very specific search for the combination of diary-n-history!
Privacy is going to be a big issue, because A9 is being very aggressive about making user identity persistent. Their toolbar, for example, requires you to be logged on. The toolbar will also log all URLs that you visit from that browser. It also copies everything you search in another SE to its own search input box. Amazon offers a share of the pi to those of its users who use A9 actively. Obviously, the user has to be signed in during his A9 use to avail of the pi/2 % discount.
I had suspected that A9 would have the same number of searches as Yahoo and Google in a year, but both the established search engines have already released equivalent features. The most interesting thing to me is that ALL of A9’s innovations are just interface features. The fact that they can improve the value of a tool, purely by tweaking the interface, to the point that it becomes an application, so many years after everyone thought that the tool was mature enough to be a commodity, is impressive and inspiring.