A method of operating a mobile device, the method comprising: concurrently running a multitude of activities on the mobile device, each of the multitude of activities being representable on a display screen of the mobile device by a corresponding live user interface; placing a plurality of the activities (301A, 301E, 301G) into hibernation; for each of the plurality of activities (301A, 301E, 301G), generating an image (152A, 152E, 152G) representative of the user interface of the respective activity; on the display screen, for each of the plurality of hibernating activities, replacing the corresponding live user interface with a corresponding generated representative image (152A, 152E, 152G) of the user interface; displaying, on the display screen, the representative images (152A, 152E, 152G) and live user interfaces of activities that have not been placed into hibernation in a linear arrangement; shifting, in response to a user interaction, the representative images (152A, 152E, 152G) and live user interfaces of activities that have not been placed into hibernation towards an edge of the display screen by displaying, on the display screen, the representative images (152A, 152E, 152G) and live user interfaces of activities that have not been placed into hibernation in a plurality of display positions that change based on a direction of the shifting; wherein shifting the representative images (152A, 152E, 152G) does not revive the hibernating activities; and dismissing a selected one of the hibernating activities (301A, 301E, 301G) based on a user selection of the corresponding representative image (152A, 152E, 152G) and dragging the representative image towards a top edge of the screen. concurrently running a multitude of activities on the mobile device, each of the multitude of activities being representable on a display screen of the mobile device by a corresponding live user interface; placing a plurality of the activities (301A, 301E, 301G) into hibernation; for each of the plurality of activities (301A, 301E, 301G), generating an image (152A, 152E, 152G) representative of the user interface of the respective activity; on the display screen, for each of the plurality of hibernating activities, replacing the corresponding live user interface with a corresponding generated representative image (152A, 152E, 152G) of the user interface; displaying, on the display screen, the representative images (152A, 152E, 152G) and live user interfaces of activities that have not been placed into hibernation in a linear arrangement; shifting, in response to a user interaction, the representative images (152A, 152E, 152G) and live user interfaces of activities that have not been placed into hibernation towards an edge of the display screen by displaying, on the display screen, the representative images (152A, 152E, 152G) and live user interfaces of activities that have not been placed into hibernation in a plurality of display positions that change based on a direction of the shifting; wherein shifting the representative images (152A, 152E, 152G) does not revive the hibernating activities; and dismissing a selected one of the hibernating activities (301A, 301E, 301G) based on a user selection of the corresponding representative image (152A, 152E, 152G) and dragging the representative image towards a top edge of the screen.