This data was taken from the "App Box Pro" app, under System Info on a 32Gb iPhone 4: 10 apps running: Free 255Mb Wired 79 Active 50 Inactive 28 All apps cleared: Free 288Mb Wired 70 Active 57 Inactive 28 Clean reboot: Free 335Mb Wired 74 Active 36 Inactive 14 I believe this indicated that the apps in the multitasking tray ARE using system memory.
I "think" they were: AppSniper QuickBank FlightTrack X-Plane 9 iMovie Phone Mail AppBox Pro Camera eWallet