It'd be very nice to be able to search for users and groups where the email or group name does NOT contain a certain string. At the moment it's very easy to search for users who you know exist but hard to search for items you're not sure are there.

For example, if you wanted to search for all non-atlassian users who belong to a group, it's not possible at the moment. Ideally you could select a group and say "Email does NOT contain: @atlassian.com".