Hi, there needs to be better documentation and examples for the search module and searchstring.
You have to look in five different places to even discover that there is a parameter for category, template, etc. that can be passed to searchstring, other than blog id.
Here's what I came up with to allow a user to choose a category if they wish:
http://forums.movabletype.org/2009/09/possible-to-search-within-a-category.html
http://www.movabletype.org/feedback.html