In order to preserve VisualHub (or AudialHub) if you need to switch computers, you need to back up two things:

1: The VisualHub (or AudialHub) app itself
2: The conversion engine

To back up the conversion engine, Copy the folder at: /Library/Application Support/Techspansion

...for good measure, you can also back up your Preferences file, containing your registration info in case you lose the original purchase e-mail. It's at:
...or for AudialHub:

As far as I can tell, the two programs will continue to work in Snow Leopard, but I obviously can't predict the future or what Apple will do in it, though.

Thanks for enjoying Techspansion's software. It's been an amazing journey, and I'm sorry I won't be making it with you anymore.