For those of Windows Phone 7 device users, you must know the 10-15 seconds lag when switching between two applications. Xda member, Jaxbot has posted a registry key that resolves this issue, although this hack comes with side effect like faster battery drain and camera app locking after performing this tweak.
Here’s the key, to hack instant resuming on WP7:-
Set it to 0 to disable dehydration (Default to 3).
After doing this, you don’t even need to restart your device, just load up an application and lock the device to see the result.