You just took a leap of faith. That link you just clicked from Twitter could have been a virus, spam, or led you to some porn site. How would you have known? The origin of the site was disguised in a URL shortener.
Twitter has a very high trust rate at the moment. Why is this? Probably because you feel as though you know the person who sent the tweet. But how well do you really know most of your followers, especially those of you following 2,000 people?
Another reason is that no one has broken the trust established on Twitter. No one has yet to post a virus to Twitter that has spread (that I know of).
Do you only click on links from people you know? Or have you been just clicking on whatever looks interesting?
Experiment:
If you found this via Twitter, tweet the twurl link below to your profile and we'll track how many people on Twitter click a blind link. Lets get a discussion going:
http://twurl.nl/7c6x37