A nice design tip posted at  Heather Solomon blog

 

"Application screens (a.k.a. "_layouts" screens) usually don't display the search in the header. There does appear to be a few screens out there that do, and depending on your design for application screens, this may throw a wrench in how your page looks.  To stop the search from showing in any application screen, add the following CSS style to your theme or alternate CSS file:

.ms-searchform {
     display: none
}"