Other authors are notified except me, good or bad sign? Recently I submitted a paper to an IEEE conference. A week after the notification deadline, I haven't heard anything from the committee yet, so I decided to email the Technical Program Chair directly. They told me that 80% of authors have been notified, the rest have to wait a bit more.

I'm not sure how is that possible, sice the quota for accepted paper is limited and the committee should make all decisions at once? For the 20% authors haven't received notifications, is the acceptance rate for them higher?
Regarding the chances for your paper, this is neither a good or bad sign. The program committee is probably still busy with making the decisions on some remaining papers, which means that both rejection and acceptance are absolutely possible - there is no indication as to which outcome is more likely.

But, exceeding the notification date by one week is unprofessional and, therefore, a poor sign for the quality of the conference. Some authors might have plans to submit the paper somewhere else, which they cannot do without the notification. Please note that being an "IEEE conference" is not a quality indicator these days, but a way for IEEE to make money.