With the Search Filter Extension you can easily set up keywords that trigger a special, limited, type of search that will filter out where and for what file types Alfred looks.
Starting today I’m giving LaunchBar a try. What I’ve discovered is that it supports a similar feature, but it doesn’t seem to be as configurable as Alfred’s.
While it’s too early to write about it, my first impression is that while both these apps are offering the same functionality they took opposite routes to achieve it.