Description:
"The following example shows that even if you have permalinks activated, that the URL for the two searchterms wordpress and consulting looks like this: bueltge.de/?s=wordpress+consulting&submit=Search. With a little function, which communicates with the redirect, you can adjust the URL. In my case the URL with the two searchterms look like this with the following function: bueltge.de/search/wordpress+consulting."
Link:
http://wpengineer.com/2258/change-the-search-url-of-wordpress/