One of the features in iOS 5 touted by Apple was the ability to quickly access the camera from the iPhone's lock screen. You would double-click the home button, a camera icon would appear next to the "slide to unlock" bar, and you would be taken straight to the camera.
This method was faster than unlocking your device, navigating to the Camera app, and launching it, but it could have been faster.
With iOS 5.1, Apple changed the workflow for accessing your camera from the lock screen, streamlining the process. Gone are the days of double-clicking the home button.
To access your camera from the lock screen now, you only need to press the home button once or the sleep/wake button to bring up the lock screen. You will notice the camera icon is now there, all the time, and you can't tap on it to launch the camera. In fact, if you tap on it the lock screen will bounce, but nothing more.
Instead of tapping on the camera icon, drag it to the top of your screen. Once you get to the top of the screen, the Camera app will load, ready for you to start taking pictures. When you're done you can slide the lock screen down from the top of the screen, or press the sleep/wake button to lock your device again.
Sliding the lock screen out of the way to access the camera is faster than the previous double-click method. If you're looking for ways to take photos even faster, check out this post that explains how you can take 800 photos a minute on your iPhone.