In my opinion, the name says it all. It's an interview, with inter- coming from the Latin and meaning "between". That means it's a two way process. You're interviewing the company every bit as much as they are interviewing you.

Fairly obviously, though, even if you're well prepared you only have a fairly basic understanding about what the interviewers are looking for, so they are just as likely to see searching questions as a positive sign (i.e. this person does his/her homework before making a decision) as a negative one (i.e. this person seems to be placing lots of conditions on accepting this job). All you know for definite is that they're trying to get an accurate picture of who you are and what you're like, so why not let them see that?