The idea of needing to search in a single and specific blog is rare, but there's still times that it could be useful. Take for example the need to search for articles that are just in the recipe blog, or custom service blog, or the fashion blog. For those times you really don't want to get results from the general news blogs (or even unrelated pages and products).
The key to this is knowing the finer details of the storefront search and making use of some fake staff members. The fake staff members is the key to this. Since you're able to filter searches by author and can assign any article to any staff member, this creates a basic filtering system.
Imagine if you make a new staff member called "Fashion Blogger" that would be posting under the "Fashion" blog only. You'd make sure that the author for all those articles is set to this fake staff member. From there, all that would be needed is for some minor theme mods to create a custom search url.
If the the customer is searching for "Pants" the traditional url would be:
That would return everything - articles, products, pages, etc. But to limit the search to just one blog, filter it by the Author as well:
Handy right? At some stage I'll add some code snippets that might serve as inspiration for coding up that special url. If you're totally stuck just leave a comment.