I'll echo the other posters. Student interviews are definitely more laid-back, though it kinda depends on the student and whether or not the interview is open or closed-file.
Here's my experience:
1. MCP Hahnemann - closed file, first year student: really just focused on getting to know me. I was able to ask a lot of practical and quality of life type questions. This interview was actually over lunch, as most of the student interviews are at MCPHU, which made it even more relaxed.
2. Finch - open file, fourth year student: this one was much more formal. The student had some rather standardized questions as well as some of the getting to know you type questions.
Just remember that at many schools the student interview is taken very seriously by the adcom, so even though it is a pretty relaxed experience, take it seriously.