I'm a Miami native and lived in South Miami all my life. The area is nice, there is a 'shady' spot right next to campus but its getting better due to urban renewal (sad but true). I used to live right near there and have never felt worried for my life one bit. UM has a pretty campus and is in Coral Gables, one of the more manicured areas. Don't bother trying to nurse ideas of walking to places because you'll change your mind the moment you walk out of the AC. It gets HOT, and I'm not just kidding here, average temps are in the mid 80s or higher in summer. 'Winter' (dry season really) is the best time, from about late October to early January, depending on when you get that first cold front to FINALLY reach you! You're going to need a car with excellent AC or you'll be miserable during the wet season. It rains a lot in the summer but it goes away really fast, usually in a couple minutes when the sun comes back out and increases the humidity with the evaporating rain x_x Oh and don't worry about hurricanes, they aren't so bad. =D
Best places to hang out are in the Grove and downtown. South Beach is too pricey but worth a visit every so often. South Miami also has the Shops at Sunset Place which are okay, I used to go for the movie theater. The Falls is also another great shopping mall but Dadeland was always my favorite.
Oh and if it wasn't impressed to you enough, know some Spanish before you go, or learn the moment you get there. If you plan on wandering around Calle Ocho you're going to need it =)