In 140 characters or less: Twitter is stealing and harvesting all of your information without your consent. #uncool
Whenever users click on the "Find Friends" feature on the app, Twitter searches throughout your phone's contacts and suggests people you know. So, no, it's not a coincidence that some random ex-hookup (whose number was in your phone) has suddenly shown up in your news feed.
This came to light when an app developer, Arun Thampi, saw that his contacts were copied, without his consent, to the social-networking site, Path. The CEO of Path, Dave Morin, apologized, and then promised that Path would start asking permission before they copied all of their information.
The Twitter app not only goes through all your private contacts, but stores your information on a server for eighteen months. Much like the clause that Apple buried in their iTunes user agreement that allowed them to track and store your movements, Twitter's actions aren't fully disclosed to the users. (As far as Apple's part of it, two congressmen have asked the company why they willingly participate in the sharing of private information, which actually violates their own guidelines: "Apps that read or write data outside its designated area will be rejected.")
Twitter responded to all the criticism by saying that they'd let their users know before they rifle and harvest all of our friends and hook-ups. But be honest, America: you'd still let them do it anyway, right? The whole point of social media is to connect; and, more importantly, re-connect with people from our past. That said, I'd like to be alerted before it happens.