I grew up in FL and moved to Pittsburgh from Orlando in August 2006. For the most part I really like it up here. I work in health care, so I never had trouble finding work. I get paid more up here than I did in Florida, and find the cost of living significantly lower. I love the 4 seasons and the cold and snow, but I ALWAYS hated the Florida heat. But coming from Miami, you'll probably find the cold weather more difficult to deal with.
I find the lifestyle much slower and more laid-back up here than in Orlando. People even regularly drive 5 mph under the speed limit up here (which drives me nuts by the way!). There is less crime up here, and violent crime is virtually non-existent in some suburbs. Overall, it's much less stressful to live here than it was in Orlando with all the road rage, violent crime, and low wage service jobs. The scenery is beautiful here with the rolling hills and so many wooded areas with wildlife right near the city. And I like the gritty feel of Downtown Pittsburgh as opposed to the antiseptic, fake feel of Orlando.
As for negatives? If you are not in healthcare you might have some serious trouble finding work here. Some of the customs and way of speaking of the locals take some getting used to (Do you know the meaning of jumbo, gumbands, slippy and the Pittsburgh Left?

) For the most part, the locals are quite friendly, but to be blunt, there are a whole lot of hillbillies up here. The people of Pittsburgh as a whole seem very sheltered and like to over-exaggerate the negatives of the area because they've never been anywhere else to compare it to. One of the biggest problems you'll likely face is finding your way around this place by car. The road systems are an absolute disaster because of the topography of the area, and the lack of signage doesnt help. Major arteries from the city are often 2 lane roads with a 25mph speed limit, so there are often bad bottlenecks and backups at rush hour. And Pittsburghers have no idea how to merge onto an interstate (because they actually have STOP SIGNS on some on-ramps! Insane!). But I think the positives outweigh the negatives, so after 2 years, I'm still satisfied with my move. I could never go back to 6 months of 90+ degree heat and $10/hour jobs in FL.