Hi!
I was just wondering if there was any plugin to add a human scale figure like that which is present at the sketch-up origin when a new file is created. It would be really useful to architects in my opinion. 
You could download free figures around the web and create your own template with them.
the issue is getting the models to automatically face the camera and scale accordingly.
discussions and sort of solutions are here downside is stil that you have to run the command or script each time you want them to face the camera. i believe it has been worked on but no idea about the outcome so far. maybe @pascal can hint out the status.
another idea if you can do with black figures only, you could use a font with human bodies and a horizontal to view style. that would solve that it keeps facing the camera for now if you can get such a font working.