Omni Software Update Stats
The Omni Group, makers of Omniweb, Omnigraffle, Omnioutliner, and pretty much all Mac software that begins with 'Omni,' has compiled a page of statistics about their customers. These numbers come via Omni's automatic software update capability, though the information about customer systems is strictly opt in, so don't put off making a todo list with Omnioutliner because you are afraid Omni is watching.
This is completely unscientific, especially since Omni won't tell us the size of the sample, but it looks like more than half of Omni's users have made the jump to Tiger. Also of note, most have a gig of Ram and are using a G4 machine.