Currently there is no way to filter devices based on the active user. Currently we're tagging devices with users as we are using the software. Seems like this wouldn't be too difficult to implement.
There is a trick. Just type "u:[username]" or "user:[username]", this will filter on logged in user. You don't have to select the search box, just start typing and hit [esc] to clear the search box. Let me know if that works. Feedback appreciated.

Yilan,
Yes, this works. Thanks for informing me. Works just as expected.
"u:[username]" or "user:[username]" not working on 0.7.28, testen on linux and win servers, ip:[ip] works great, but we need username filter too )
Confirm bug too.
u:[username]" or "user:[username]" not working