I've been watching the processes on my iPhone very carefully while running Pandora and TuneIn Radio, and it seems that audio apps, at least, are actually backgrounded. When Pandora is running in the background, for instance, it continues to use almost as much memory as when it is in the foreground. Its behavior is pretty much identical to that of the native iPod app: most of the work of the streaming seems to be done by Apple's 'fairplayd' process (and of course CommCenter, which is handling the streaming) but Pandora remains memory-resident and there are periodic spikes in CPU usage.
I am really curious as to how TuneIn Radio plays WMA streams in the background. Clearly it has to be handling the decoding itself, since the iPhone doesn't support WMA natively, but I can't really see it using much CPU at all. It really has been well implemented.
One thing that does surprise me is that Pandora and TuneIn remain in memory when closed even if they are not currently playing anything. I'm sure that iOS will close them if it needs the memory, but that's not how I expected it to work.
I am really curious as to how TuneIn Radio plays WMA streams in the background. Clearly it has to be handling the decoding itself, since the iPhone doesn't support WMA natively, but I can't really see it using much CPU at all. It really has been well implemented.
One thing that does surprise me is that Pandora and TuneIn remain in memory when closed even if they are not currently playing anything. I'm sure that iOS will close them if it needs the memory, but that's not how I expected it to work.