The first reason for using the Quero toolbar is that it does not occupy any additional screen area like a normal toolbar would. It uses the free screen area to the right of the menu toolbar, but if you do not use the menu toolbar then I guess this is a problem.
The second reason for using it is that the search provider is not fixed to a specific provider, like Google or Yahoo toolbar are.
The Quero Toolbar allows you select your search provider from the right most drop down list box, i.e.
Google, Yahoo, Bing, etc.
You can add your own search providers to the list or delete any of the standard providers listed.
I just selected Google as my default.
Options allow you to setup the Search Box to only display your entered search text just like IE 8 worked.
If you only want to search using Google then just use the Goggle toolbar.