Posted on DailyTech, who sourced the information on AppleInsider, so I am not sure how reliable the information is. Normally I do not keep up with iPhone related rumours, despite owning one, simply because I am rarely the first one to update (in fact, I've only updated twice, and both times were so that I am able to update *one* particular application I use all the time).
But I suppose that it would make sense for them to finally include this feature. Bit late for the launch of the iPad, but better late than never, and it is a common criticism if I am not mistaken. And with the 3GS, the iPhone is now more suitably better equipped (hardware wise), to deal with running more than one 3rd party application. There are two applications that I -must- have, and one permanently runs in the background of my jailbroken 2G phone. I wouldn't say it's a resource hog, but it's enough of a resource drain to cause, but it's enough to cause more demanding applications to run out of memory. I wouldn't expect the 3GS, with twice the memory to run into that problem (well, unless you pick two fairly 'heavy' applications).
Well, for me, it's not the feature I want the most. That'd be a native Kanji IME pad: the existing one is designed for traditional Chinese and far inferior to Windows' IME pad for Japanese. Yet I reckon that it's an important feature for everyone else who might consider an iPhone/Touch/Pad this year.