I got it to work earlier today. I used Xcode to make modifications to Desktop Manager, and Emacs to adjust smack.pl to work on my PowerBook 12'. It was a bitchy and time consuming process, especially for somebody who almost never uses Xcode nor knows how to program in anything beyond Java.
The biggest problem is adjusting the sensitivity. The video shows it working surprisingly well; my PowerBook 12' usually refused to sense taps on the side of the screen no matter what the numbers were at. The biggest problem with this whole thing is that using the laptop on anything but a flat surface causes the thing to start sensing "smacks" like crazy. The installer can be fixed easily, but making the concept itself work well is either going to be a very clever programming job or downright impossible. I also found that using a desktop switching hotkey, such as apple + -->, was far easier even if the touch thing did work.
Quick guide to installing:
NOTE - Intel Mac users should skip steps 1-7, as the official source code I linked to doesn't compile on Intel Macs. Your only option (that I know of) it to use a user ported version of desktop manager, such
as this one. I have not tried these pre compiled versions myself, but have heard that they work.
1) Download the latest Desktop Manager source code:

2) Extract source code:

3) Open Xcode (you should have this, if not get it from your Mac OSX install CD) and either go to file --> open or just hold apple + o. Select the directory you extracted the DM source code to and hit open:

4) Type "WorkspaceController.m" in the search box. It will bring up only one result. Double click on that result:

5) Scroll down to you reach the init portion of the code. Where pictures, cut and paste the following:
[[NSDistributedNotificationCenter defaultCenter] addObserver: self
selector: @selector(selectNextWorkspace)
name: NOTIFICATION_NEXTWORKSPACE
object: nil
];
[[NSDistributedNotificationCenter defaultCenter] addObserver: self
selector: @selector(selectPreviousWorkspace)
name: NOTIFICATION_PREVWORKSPACE
object: nil
];

6) Click the button "Build and Go". In the box that pops up click "Save All":

YOUR MODIFIED VERSION OF DESKTOP MANAGER WILL NOW COMPILE. DEPENDING ON THE SPEED OF YOUR MAC, THIS WILL TAKE A COUPLE MINUTES. 7) When it finishes compiling, it will automatically launch. You will know this when desktop manager starts. How just hide Xcode (apple + h).

8 ) Now, download 2 files.
AMSTracker...

...and download and extract a
wonderful ZIP of smackbook itself:

9) While I used Emacs, for the sake of simplicity we will use textedit to modify the perl file. Go the the extracted smackbook directory, right click on "smack.pl", click "Get info", and replace the extension ".pl" with ".txt", and hit enter. In the box that pops up, click "use .txt". Now double click on the "smack.txt" icon, and it should open up textedit.

10)If you have an iBook or PowerBook, replace the line "my $x = $a[1]*256 + $a[0];" with "my $x = $a[0];". The line "if(abs($x) > whateverthis#is && $stable > 30) {" defines how sensistive it is, "whateverthis$is" being the sensetivity. If you have a MacBook, leave it as default (I think). Users of the iBook or PowerBook may wish to turn it down to something like 10.

Save the file when done.
11) After saving, go back to the info pane for "smack.txt" and change it back to ".pl":

12) Open the dmg "AMSTracker". Drag the file "AMSTracker" out of it and into the smackbook directory.

13) If you made it to this point, congradulations, your half way there. Actually, that's a lie.
Open Mac OSX Terminal. Type "cd", space, and then the path of the smackbook folder. An easy way to do this is just drag the folder onto the terminal window. When your done, hit enter.

14) Type "perl smack.pl" into the terminal and hit enter.

If everything went correctly, your laptop should be going crazy and/or working properly with smackbook.
If it outputs anything but "simultating AMS hardware" and "self descruct activated", you are good to go. If you get the simulating error, you either need to reboot your laptop or don't have (working) SMS hardware. If you get the self destruct error, run away from your laptop as fast as you can run.
I will answer some questions if I have time. Contact me using an instant messenger; my AIM is katoblepas and my MSNM is spamthis*at*deflektor.com.