I already talked about my open house experience at OSU (Ohio) with math_applicant, but I'll post my feelings here.
I absolutely loved my visit to OSU. It seems like it's a great community of graduate students and mathematicians, and, though I didn't meet many graduate students and professors, I didn't meet anyone I didn't like. The possible first year cohort was a blast to hang out with; if you and I both end up going, I think we'll all enjoy each other's company, have Friday outings and the like. The campus is HUGE and pretty. The 7 story math tower is marvelous. I also met a prospective advisor; he was VERY excited to work with me, and if I go there, I know it will be a very positive experience working with him.
I was told that it's an environment of collaboration; there are student-led "reading" seminars in algebraic geometry, ergodic theory, and other disciplines, even! Also, the qual situation is relatively easy (Baby Rudin and abstract algebra at a similar difficulty, the algebra qual considered the easier of the two), but the coursework is considered pretty tough. Teaching duties: they typically give "preference" to first years in that they get two classes to teach of the same section, relatively close to the math building, of first year calculus or a similarly easy course.
Hope this helps some people!