In the maniphest advanced search, selectors "In All Projects", "In Any Project", "Not In Projects" are not obvious to all users and take three rows of space. They can be replaced by a single "Projects" field accompanied by a dropdown to select AND, OR, NOT operator.
This is standard solution in many search forms, as far as I can see. Compare http://catalog.loc.gov/vwebv/searchAdvanced (uses a radio button).
Downstream report: https://phabricator.wikimedia.org/T1378