The Verge forums user Sentry posted the concept art you see above for the (underutilized) iOS task switcher, and I think it's awesome. Sentry's vision adds a lot of worthwhile information to the multitask bar without sacrificing the clear layout.
The app thumbnails are great, but I really like the various controls for music, WiFi and Bluetooth. It's such a pain to have to dig down into the Settings app every time I need to switch one of those on my phone or iPad, and having them accessible with just a double-tap and a swipe would be excellent.
I already heavily use the audio controls that pop up when you double tap the iOS Home button while your device is locked, and sliding them into the task switcher seems like a no brainer. iOS 6, of course, was just released, so we're now waiting for Apple to tell us what's next with the portable operating system. Hopefully, an excellent revamp of the task switcher like this is being worked on right now.