At the moment I'm sitting on interview panels quite frequently. Let me start with saying two things: at least where I work, the people on the panels are normal "human beings" who understand a lot of things that is going on with candidates, e.g. family, delays, problems etc. Second, a lot of red tape applies in bigger companies and that can sometimes effect how the decision-making process goes, e.g. you must ask the same questions to every candidate, even if that is maybe not really logical, everything needs to be accountable and absolutely comparable, you may not make any assumptions, etc.
In general, in my experience after shortlisting the CV/qualifications aren't that important anymore - otherwise people wouldn't have been shortlisted for an interview. In other words, everybody shortlisted has the required qualifications for the job and is theoretically employable.
Favouritism probably exists, but the more the process is accountable and overlooked by HR departments the less it is likely to actually happen. I would argue that, unlike the views people have taken in this thread, usually HR involvement helps to keep everything fair. Of course you do hear stories from other places etc., and I won't be so naive to suggest that everything is always perfectly fine.
The interview is really important and is best approached with a natural attitude. If you try to bendover twice to make something work that you're not, it will be much harder to be convincing.
