The latest speculation is that Apple will allow one or two 3rd party apps to run in the background. Currently, Apple lets you run the iPod music functions in the background, but no 3rd party apps have this capability. The servers side notification support coming in iPhone 3.0 may address the needs for some apps, such as IM apps, but there are still some others that would benefit from running in the background on the iPhone.
These speculations are tottally based upon the fact that Palm Pre, to be released soon, has Background application support or rather full multitasking. in order to meet competition, they might have to come up with this. Though, unofficailly, iPhone already has “backgrounder” that lets you run apps in background.
I think the most valuable type of application to run in the background for me is a VOIP and IM application which remain connected to internet all the time and give me the real experience. SOme other most desired would be like running bulky appliations in background by putting them into some low memory state for quick execution next time.