First, sign up here: to get a discount, use code: FYuu9gSC9b and you will have ZERO fees for months.
Next, the Ethereum token can be traded in ETHUSD and ETHBTC, both pairs are active on the "Exchange" side of the site.
At launch, margin trading is not active for Ethereum on Bitfinex.
A Bitfinex agent has said that margin trading and margin lending will not be available until Bitfinex is comfortable with the liquidity on the normal spot trading part of their exchange.
The fees you pay will be 0.2% at the most, and there are maker/taker benefits:
Here's more screenshots: