I've tried animating the d attribute of a path but it does not work.
Created attachment 24094 [details]
The subject of this bug appears to be incorrect (or no longer correct). It is possible to animate the d element for a path. (I'll attach a test case, also available at http://phrogz.net/SVG/multi-path-anim.svg.) I think the bug with the original attachment is that begin='click' does not work.
Created attachment 49496 [details]
An animated 'd' attribute on a path.
The attachment has an animated path (black) and two animated lines (red and blue); the animation for one line is nested, the other uses xlink to reference the element. All three use a pair of animate elements. All three should look identical (other than color).
Additional test case verified to work as expected on Safari 4.0.4 (531.21.10) on Windows, and also Chrome for Windows 184.108.40.206 beta (38071).
Thanks for verifying it Gavin.