Giddy 3's timing is done via a timer which is not tied to the screen refresh rate. It does this so that it always runs at the correct speed. The downside is that it will never be super smooth.
The Wii has the advantage of only ever being 50 or 60Hz (like the old Amiga), so that port uses VSync for perfectly smooth scrolling.
If someone wants to add a vsync mode, get in touch. I don't want to open source Giddy 3, but i'm happy to give interested developers access to the SVN if they agree not to spread the sources.
