Looks like TomTom have released an update to TomTom Navigator 6 for UIQ3 (P990/M600/W950). This update can be found by plugging your phone into your PC whilst TomTom Home is running. Unfortunately it looks like TomTom Home is actually unable to install the update though.
So here’s my step by step guide.

1. Plug your phone in to you PC in File Transfer Mode and run TomTom Home.
2. Download the update.
3. Unplug your phone.
4. Uninstall TomTom from your phone.
5. Find the cab file which would have been downloaded on to your PC (should be My Documents / TomTom / HOME / Downloads / ttn.symbian.UIQ3.6021.8120.cab)
6. Use Unzip software to unpack the cab file.
7. Plug phone back in to PC in File Transfer Mode.
8. Via MyComputer open the Memory Card.
9. Drag-and-drop the 4 folders and install.bif file on to your Memory Card (say yes to any Replace prompts).
10. Unplug your phone, wait a short while and follow the prompt to install TomTom.

To be truthful the only difference I can see is the option to switch between Left and Right hand modes, and I’m guessing better memory handling, but not much else.