Switching between suspended apps in Windows Phone 7 can be laggy as the apps are dehydrated (status saved in internal storage) when suspended. When you go back to a suspended app the Windows Phone 7 OS has to retrieve the status from the internal storage and resume the application, this is what takes a bit of time. Jaxbot @ WindowsPhoneHacker found a registry hack which eliminates this lag.
You can see this hack in action in the YouTube video below, going back to a suspended app is snappier than usual:
This registry hack requires a dev unlocked / jailbroken Windows Phone 7 device, to unlock your device follow our instructions @ How to Jailbreak Your Windows Phone 7 Device.
Be aware that using this registry hack will increase the memory usage of your Windows Phone 7 device and may have other side effects (battery life etc.).
Then edit the following registry key: HKLM\Software\Microsoft\TaskHost and set DehydrateOnPause to 0 (default is 3). You can edit the registry using the Registry Editor app @ Registry Editor for Windows Phone 7 Beta Testing.
You can get more information about this instant resuming Windows Phone 7 hack @ http://windowsphonehacker.com/articles/exclusive_instant_resuming_on_windows_phone_7_hack-03-19-11.
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