I find the phenomenon of having to verify that I am indeed human on certain sites slightly creepy. In my opinion digg is the most friendly of the lot compared to the curtness of say reddit. See for yourself.
This has an easy and apologetic tone to the whole proceeding. Compare it to this. Shame on you reddit!
Yahoo finds the middle ground between insult and etiquette.
I will tell you if I am human if you ask nicely.