Question #2 over at Ask a Manager. A person wants to know how they know if they did well in an interview. Of course the blogger's answer over there is there no way to truly know and that if you think you did well you may still not get the job or you might do bad and still get the job. It's best to read her answer to that question.
I did use to have an easy answer to this question. Again I've had interviews such as this one I wrote about earlier this year where I thought the interview went great but still didn't get the job. Although in that case it was still a dodged bullet.
Still, I think it's easy to gauge from interviewers whether or not they like you. Unfortunately it's still hard to say whether or not they'll offer you the job. It seems in some of the comments over at Ask a Manager you may get an offer and the employer could always change their mind.
These days, however, only speaking from my experience it seems I'm wary of the statement that they're continuing to interview other candidates. Now again this probably isn't something you should consider too much of because it's only fair if there are other candidates lined up. Besides the odds may still be in your favor or it may not.
BTW, for additional reading another link was offered with Ask a Manager's response. If you can't help but consider your chances for getting the job this post should help you keep things in perspective. One answer to that is even if you're sure you got the job continue applying until someone gives you a solid job offer.