I have just installed Natty on an Intel Celeron single core CPU with 1 GB RAM without a 3D graphic card and Natty is running on Classic Desktop instead of Unity.
I have to force turn off and restart the computer system to recover.
Maximizing, minimizing and restoring do not freeze the system. Only when I tried to click and drag the border to resize my computer system freeze with the window having a orangy tint.
Otherwise Natty run along nicely for now.