I have been waiting for the Windows Phone 7 multitasking since the day it launched. Till today, I am still waiting for the simple function of copy and paste. Now, if you are a developer, you may want to try out a simple registry hack to allow Instant App resume to you WP7.
You can open an app, turn off the screen. When you turn the screen back on, normally, you should be waiting for the phone to “resume” which takes some time.
With this registry hack, you can get back to the last instance instantly. The hack involves changing the “DehydrateOnPause” registry key value to zero which will rid of the app dehydration / rehydration process.
This, of course, is not approved by Microsoft and to edit the registry, you will need a developer phone to do that. Here is a video.