I know that even on intel macs, avidemux has its uses (and its users). However, avidemux may have seemed broken after upgrading to Lion or Mountain Lion from Snow Leopard. While avidemux is still unstable at 2.6, 2.5.4 can be modified to work as normal. I even found it ran snappier and with more stability after the modifications.
To get Avidemux working select avidemux2.app in finder , right click and show package contents.
Delete the files libxml2.2.dylib and libiconv.2.dylib from the Contents/Resources/lib folder.