Warning - Portuguese Man-O-War out da wazoo!
 

Just came back from a session in south Palm Beach County. There were hundreds of Portuguese on the beach. Heading out I saw on average one per 30 square feet although at times you might see five clumped together. There are a LOT of these guys on and near the shore. It is strange to see so many with a south, near sideshore wind. Usually you see more with NE to E winds here. We haven't seen that many Portuguese this season, looks like they're making up for lost time.

If I am expecting Man-O-War I usually wear a full wetsuit and keep looking to windward. If you get dosed badly enough or are vulnerable you can go into shock after getting stung. Not a good thing if you are still well offshore. There are preparations in drug stores specific for jellyfish stings, otherwise vinegar, Adolphs Meat tenderizer can be applied topically to the sting area. They can hurt like a mother so the best course is to avoid being hit by them.

http://www.fksa.org/albums/album580/beach.jpg
They were a lot thicker than this in some areas of beach and about a 3/8 mile offshore.

I understand they are thick in the Florida Keys as well right now.