I am not sure if A9‘s product placement is completely understood. They add value to the typical Google search. The value is acheived by focusing on websites that you think are absolutely relevent to the query your about to place. On the other hand, selecting those sites from a possible list of thousands (or even 5) is tedious. I would not use A9 for my everyday needs.
Siddharth wants to know why not use A9? If you have some insight into the issue, head over to his blog and let him know.
Other products offering customized search: