I found Openoffice to be very similar (but a bit more complex) to Google docs. Google docs, however, is based online and can provide more connections between users. This can be especially useful in writing collaborative assignments. This gives Google docs the advantage over Openoffice.
I have used Google docs in several of my classes at UHCL. This has been an incredible tool for working with classmates. I only wish that I would have known about it earlier.