It looks like the taskbarThumbnails might be leaking memory. When moving the mouse across the taskbar viewing the different thumbnails the memory usage increases by quite a lot (viewed in the taskmanager (Windows) ). I made an example script to illustrate the resource usage. Test scenario: 20 windows; 1 Playground, 19 Nautilus browsers (these are minimized). =============== Create Test Scenario ======================== 19 timesRepeat: [ Nautilus openOnClass: Object. World doOneCycle. ]. World doOneCycle. World submorphs select: [ :m | m isKindOf: NautilusWindow ] thenDo: [ :m | m minimize ] ===== Enumerate the mouse moving from one taskbarButton to the next ======= | delay | delay := [ :msToWait | | t | t := Time now asMilliSeconds. [ (Time now asMilliSeconds - t) < msToWait ] whileTrue: [ World doOneCycle ]. ]. 20 timesRepeat: [ World submorphs detect: [:m | m isTaskbar ] ifFound: [ :taskbar | taskbar orderedTasks collect: [ :task | task morph ] thenDo: [ :morph | | button | button := (taskbar taskButtonOf: morph). morph taskbarButtonEntered: button event: nil in: nil. delay value: 100. morph taskbarButtonLeft: button event: nil in: nil. delay value: 100 ] ]. Smalltalk garbageCollect. ]. ============================================================ Results: (Newest Win vm -> Image 50377) opening the 20 Windows RAM used is 70MB. 1 iteration: 93MB 20 iterations: 130MB \ 190 MB when garbageCollect is commented out. Should the resource usage be that high? (a taskbarThumbnail is deleted before the next one is shown...) Best regards, Henrik