It is real multitasking. The OS does nothing to inhibit applications from running anything in the background. But most of developers, as a courtesy to our users, usually stop any non-critical functions from taking place when the application is backgrounded, to save battery life.
While it is a nice show-off feature to have, say the camera work in the background and show through the thumbnail you can't take a photo while on the switcher so it's better to have the camera hardware turn off while the camera app is in the background.

I thought about this extensively for ρcam. In the early development versions the camera wasn't turned off when the app is in the background, and that was cool. But taking into consideration the really quick camera startup of the N9 the following two usecases emerged:

If ρcam doesn't suspend the response tome after switching to it would be instant, but it would be consuming loads of battery in the background making the backgrounding operation useless except for very small interruptions (seconds at best) and thus forcing the user to close the app when not in use. The next time he will want to take a photo he will have to wait for the application to load again. Finally some users would get surprised finding their battery dead in a very short time.

If the camera suspends while in the background, just swiping away (or locking the screen for that matter) will ensure that the phone is in a power-friendly mode and in order to take a photo the user just needs to unlock or switch to it. The camera module of the N9 powers up almost instantly so for snapping around every now and then when on a trip this is a much quicker way, than having to launch the app each time.

I chose the second solution, and that is what most developers finally choose. This is still better than the limited multitasking of other platforms as it can be evaluated case-by-case, like above, instead of the OS forcing restrictions upon developers. If there is a point in being able to run in the background (video app comes to mind, so one can listen to music videos while doing something else) I'm sure the developer will consider it.

Finally we can run daemons who work in the background and enable functionality of many well known applications. This is not visible, but it enables functionality not permitted in other platforms.