I use Octave for educational and research purposes. Already, Octave can replace most of my work in Matlab so I am mostly satisfied with current compatibility (in general language, optimization, and statistics). I thank everyone including all the eager users.
The main reason I started looking for an alternative to Matlab was its lack of guarantee for backward compatibility. This affects my teaching greatly. For example, if I give code for students there is no guarantee it will work, given that the newest version in the University was not the same I developed with (which is most often the case). This created a lot of frustration and I hope Octave would not make me face such a possibility. So backward compatibility is a must for educational purposes.