Does iOS 4 multitasking really use more battery life?

I got the impression that unless you were using something like Pandora that's actually churning CPU and IO in the background, the new "multitasking" isn't really leaving multiple apps open. It is simply freezing their state in memory so they would load quickly where you left them. Google is conflicted on the issue. Does anyone know for sure whether all those apps in the taskbar are alive and causing battery usage? Should I be vigilant about closing them (the interface is cumbersome) if I care about conserving power?