Ethereum seems to be the hottest crypto around as of late. The price has doubled multiple times in the least couple of months. Its been so hot that one of the biggest Bitcoin exchanges, Bitfinex, has decided to add it on March 14, 2016, at noon UTC.
According to the official announcement, margin trading will not be activated right away. Once they are comfortable with the size of the order books, leverage trading will go live. (They say it could be less than a week, it all depends on the users)
Bitfinex requires no ID as long as you cash in and out using crypto. If you want to fund your account or withdraw using Fiat, you will need to identify yourself. If you are curious to learn how margin trading such as going long and short. Check out this video, its very simple.