Florianapolis is a relatively large city in the south of Brazil. In the south of Brazil, during their relatively mild winter (July and August), it can get a little cool. For Floriananpolis, that means 50s and 60s for those 2 months. The rest of the time, the city is essentially a warm and beautiful island resort. There are cities in Brazil with problems (Recife, Sao Paulo and Rio), but even those cities are relatively safe, if you avoid the slum areas and dress casual/native and avoid wearing expensive jewelry. I've visited most of Brazil (~20 times in the past 7 years, and I've stayed in Brazil for a total of ~12 months during that time) without any problems.
Florianapolis is a lovely city, with lots of beautiful beaches. The hotels are cheap (~1/3 that of the USA), the food is cheap (restaurant costs are ~1/2 to ~1/3 that of the USA) and the cabs are relatively cheap (~2/3 that of the USA) even though gas is 50% more. Imported booze is expensive, and electronic items are expensive. If you have a friend in Brazil, bring them an bottle of interesting liquor, or an electronic gift - electronic items are 2 to 4 fold more expensive in Brazil. The city has a nice little market for fruits and veggies, and they have another little market for arts, crafts and clothes. They have "style" in Brazil and the clothes are cheap and can be very nice, so it is a great place to shop. I have been told that they have the best women's shoes in the world. My wife get's positive comments on her Brazilian shoes all the time in the USA. Buy your sun screen lotion (30+ if you are very white) in the USA - pharmaceuticals and most cosmetics items are much cheaper in the USA.
Other great cities to visit are in the northeast (Natal, Joao Pessoa, Salvador, Recife, etc.). Most Brazilians that can travel for vacation, go to the Florianapolis or cities in the northeast of Brazil.

Surfers and wind surfers like Florianopolis because of the wind and waves. That is understandable, as is also understandable why Argentians favour it. It's close to their country, and they don't have many nice beaches. But I don't see why any other tourist would prefer to spend hollidays in Florianopolis than on the beaches of Rio, Sao Paulo, Bahia, Ceara or Fernao de Noronha.
I went to Florianopolis to spend 15 days, but came back on the 5th. Couldn't take it any longer.
To start with, it doesn't look like you are in Brazil. No Samba or Bossa Nova playing anywhere, no tropical vegetation, no warm sea, and all you see are Argentinian tourists or blonde locals.
The north beaches are too crowded while the south beaches are empty because they are dirty, windy and the sea is too cold.
There is a lot of traffic, and no sinalization on the roads. You get lost all the time. The architectural style is as chaotic as the traffic. No identity.
The food is horrible. Didn't managed to have one single decent meal. I was even served bad oisters at the hottest spot of Jurere International, the hippest beach.
Restaurants and hotels are as expensive as is Sao Paulo and Rio, while much inferior in quality.
It is allways windy wich doesn't let you relax, but if the wind stops it's even worst because the mosquitos won't stop at nothing. You can use as much AUTAN or OFF you want, they will bite you anyway.
What can I say? I'll never go back.