What is the perception of students who take a gap year between their graduation and starting graduate school? I am an undergraduate mathematics major, entering my fourth year. I plan on applying to graduate school, but I have not yet taken the GRE exams, and there a few key courses (Topology and Algebra in particular) that I have not taken yet, so I am hesitant to take the Advanced Math GRE too soon. (If you're wondering why I haven't taken Topology and Algebra yet, it's because I was trying to secure a CS degree, which sidetracked my mathematical studies last year. It was a healthy branching out experience, and one that helped me realize my true academic passion.)

My main question: what is the perception of students who take a gap year between their graduation and starting graduate school?

I think I will take the GRE tests this fall, a) for practice and b) if I score high, then I might as well apply sooner rather than later. However, I ask this question to gauge how much energy I should put into preparing for the tests this fall. If I hear, "You should really do your best to avoid any gap in your education," then I will work my butt off in preparation for the tests. But if I hear, "It's totally okay take a gap year before going into graduate school," then I would give myself more freedom in terms of my non-standardized-exam studies, extracurriculars, and in general social activities. I figure the answer to this question won't be as cut-and-dry as I hope, but any advice would be appreciated!

Just to clarify, my gap year would not consist of me sitting at my desk taking practice GRE exams all day... That would be a pitiful use of my time. I definitely plan working either as an intern or a research assistant at a successful organization. It seems like the general consensus is that taking time off is okay, and potentially beneficial, assuming you actually do something in that gap.
When I was looking into this for a former student of mine I spoke with the head of the graduate program at the US Top 20 program I was working in at the time. He actually viewed a gap year as a good thing. His rationale was that students who had held jobs and managed to live for the gap year were more likely to have the work habits useful in graduate school. 

When it comes time to write your applications you just have to remember to explain how that year has made you a better candidate for their program. It might not be more math that you've learned by it may be maturity and a renewed sense of purpose. If you chose to take a year off do something worthwhile and don't just study for exams.