When Careers 2.0 first popped up, I thought it was an excellent concept. Invested employers could appreciated programmers who liked working collaboratively, get a very real sense of the technical skills of potential candidates, and inspect a person's development over time, all before initial contact.
It seemed like a great reward for those who had invested energy into StackOverflow.
But last I had checked the site, the vast majority of employers requested a resume be submitted via e-mail, and I never received any contact directly through there that referenced my activity on SO.
Although I appreciate Careers wants to appeal to as many employers as possible, and therefore many will not know about SO or have the time to delve so deeply into employee history, I feel the emphasis on PDF and e-mail-submitted resumes removes its killer feature.