Version 1.04 (in my repository, see signature) now has functionality similar to Alt-Tab. First enable it with:

gconftool-2 -s /apps/osso/hildon-desktop/key-actions/ctrl_backspace_in_tasknav -t int 5

Then, when pressing ctrl+backspace, leave ctrl press. Every press of backspace rotates the displayed task windows. When you release ctrl, the upper leftmost windows is switched to.