i know that it can give problems to some of the more memory intensive apps. in particular, the gps navigator map app i use tended to start playing up after a while (when i was testing over the past few weeks) - but i noticed i had about 20+ apps all "running" in the background, once i quit most of those the traffic app started picking up my location correctly again.
but i guess that's the case with all multitasking - whatever the device, there's always going to be a finite amount of memory available.
i haven't ever been aware that it's killed inactive background apps though. in all my testing, i think they always stayed open until i killed them. that might be a feature of the latest full release perhaps?