From what I've read about Android and from what I've seen in a friend's HTC Hero, Android practically does not multi-task:

Since Android's apps are in java, you only can run java apps. Now, according to an article I'd read about Android programming (I don't remember where, but have a look at the activity lifecycle here) and from what I've seen, Android freezes java applications when they are left in the background. The friend of mine also claimed that it swaps-out the application to free memory (but I can't understand how it can do that).

Also, how are you supposed to install a new media player in Android? Can a Java program practically play a hi-def video? From a test I performed the HTC Hero could not play a 720p video (as avi and mp4) I created, most probably because of missing codec. This video runs from mplayer under N800 (but very-very-very slow). Can you do that with Android? I don't believe that there will ever be any video-playing program written in Java to extend the video-playing functionality of Android.

As for the hardware specs: that's not an OS issue. However, since you mentioned them: I'm more-and-more pleased by the fact that N900 will have a resistive screen. Being able to use a stylus is a great advantage. It is *very* slow and uncomfortable to do some tasks with your finger. Just try to type a long URL using an iphone.