If you want to do a simple ANDed search, there is another way to accomplish this, without actually using the search interface.
By going to one of the tag pages, using
[nhibernate] as an example, if the additional tags you want to search for are popular enough within that tag to show up on the right side of the screen, clicking on one of those tags automatically adds an AND to the filter.
So if you're browsing questions in
[nhibernate], clicking on the
[mapping] tag on the right side takes you here.
This is a really easy way to browse through questions, and without doing a lot of typing. As I mentioned, the tags you're looking for do have to be popular within the subset of questions shown in the list, but once you've narrowed things down by 2 tags, the list is generally short enough to just browse through all the questions to find what you're looking for.