I just need to say that at least for my setup, these drivers work just as they should.
I've used and Kensington trackballs since the Turbo Mouse 4.0 was a new product (deep into the ADB days), and the hardware has stayed great, in my opinion. The OS X software is no-doubt still less feature-rich than it was in an OS 9 version (version 5.x I think?), and I was very worried that this 3.0r1 version wouldn't work at all for Intel Macs, from the reviews here, on VersionTracker, and elsewhere. But for my Mac Mini Core 2 Duo, running 10.4.10, with the Turbo Mouse USB it works just fine.
It's as configurable & reliable as it was on my older PPC Macs. The acceleration works accurately, and the 'Slowly' and 'Quickly' thresholds are just where they should be, when I move the cursor slowly, it can really go VERY slowly, and ditto with quickly.
So I just wanted to say that my results actually installing it, were very good.
This, after fearing that it wouldn't work at all on Intel Macs, and thus trying USB Overdrive and SteerMouse, neither of which could do the very helpful chording feature that Kensington's MouseWorks driver can do (which adds 2 more button-functions to my 4-button trackball).
So you've kept me happy Kensington, though I'd love it if you could add some speed/acceleration options for the scrolling feature of my model trackball. I've had to settle for the Control-Drag feature in the fantastic program Saft, for great scrolling in Safari.
My advice is try it on your Intel Mac, if it doesn't work, use their good'n'simple un-install app included with the installer.