Assuming you're using fully-compliant apps (Nokia apps, at least, not sure how many others), when the tablet runs out of memory, it doesn't give you an out-of-memory error. It just closes one of your open (but not foreground) apps, after telling it to save its state quietly, and receiving confirmation that the state is saved.

In the task navigator, the icon is overlayed with the number of windows (if > 1) open, you know? Well, when it closes an app due to short memory, it keeps the app there, and overlays a "ZZ" in the same corner. Now if you click on that app, it will restart (closing another app to free memory, if it has to) and reload its state. S.l.o.w startup, of course, but it comes back just like you left it.

If all apps that can save their state are closed, leaving only apps that can't/won't, and there's still no room, then you get a message indicating that you're out of memory, and asking you which app to close.

So you may have experienced low memory problems, but not noticed it, because with "good" apps, it's handled as smoothly as possible.