I guess I just don't personally see it as wasted space.
One doesn't want anything being touch-sensitive on the device when it's locked other than the unlock mechanism. So if there was more information shown, there'd be no way to do anything about that information (reply to it, clear it, delay it until later, etc) without unlocking the phone and then navigating back to the information that triggered the information in the notification through whatever app was doing the alerting.
Maybe I'd feel differently if I had a passcode/password on my phone; but, since I don't, unlocking is just a button-push-then-swipe that happens unconsciously during the transition from my pocket to in front of my face. So I might as well use the 'real' app by the time I'm ready to do anything on the device.
The exception of course is the time/date which are already shown - that's information that is strictly received by the user, who doesn't have to do anything (in the device) in response. So maybe adding things like the weather as an option makes good sense... but I don't personally think I want actionable things like emails/tweets/etc on the lock screen.
Of course, there is on iPhone the "alternate lock screen" that appears when you double-click Home and music is playing. Maybe there is room for an expanded not-quite-unlocked mode when you double-click Home to unlock?
I personally expect there to be changes to the notification system in iOS 5, but I won't be surprised if the lock screen stays approximately as-is. Wouldn't necessarily mind being surprised though!
This area must be on the list of improvements for Apple with the next software shipment. There is huge opportunity to use this space as a communication hub, something all iPhone users would benefit from.
