Anyone who’s into compositing should check out Conduit, a new plugin for Motion from dvGarage (which is essentially the PixelCorps). It adds nodal compositing to Motion, so that you can do Shake-style node trees to build your composite, but take advantage of Motion’s realtime playback. The interface is well done, if not entirely HIG-complient.
In any case, if you’re at all interested in high-end compositing, this is a great way to jump in. While the cost is less of an issue now that Shake is only $499, the interface of Conduit is much less overwhelming, so you can focus on wrapping your brain around nodal composites instead of learning an antiquated interface.
One imagines that whatever product succeeds Shake will be very similar to this.