SAN FRANCISCO (Reuters) - Facebook filed on Wednesday to raise a targeted $5 billion in a hotly anticipated initial public offering, setting the stage for Silicon Valley's biggest-ever IPO. The world's largest social network, a dorm room project for Harvard dropout Mark Zuckerberg that exploded in popularity and vaulted to Silicon Valley's top tier within 8 years, said in its preliminary filing that its net income rose 65 percent to $1 billion in 2011, off revenue of $3.71 billion. ...