Hi turner,
Thank you for sharing your feedback with us. I will forward your idea to our GSA team. Ideally, as more users utilize the federated GSA search box, the ranking intelligence will improve based on crowd-sourced user selections.
If you'd like to manually filter search results by source, simply click on one of the source filters on the right hand column of the search results page. For more information on GSA search functionalities, please take a look at the following TKB article:
http://community.arubanetworks.com/t5/Community-Feedback-and-Support/Search-Global-and-Community/ta-p/56518
Thanks,