So, I recently upgraded my firmware(long story short, it stopped some apps working properly, no biggie). Previously, I applied the Multitasking hack(jailbreak not required) on Windows, via iPhone Explorer(can't find the link right now). After restoring to the latest firmware, I discovered that the hack is preserved in the device backup. So basically, I have stock 4.3.4 firmware, with the multitasking gestures still enabled! There's no toggle in Settings, but I wouldn't want to turn them off anyway.