^This. Bter was giving daily interest to people for keeping their Bitcoins in their wallet and then one day they were apparently "hacked".
The sites which are advertising that is to lure people in and once they accumulate enough funds they run away. Best just keep your funds in your wallet.
I doubt Bter was a scam. Personally, I believe they that they were genuinely hacked although I guess it's pretty hard to prove it either way.
For all I know they are using the fund to perform arbitrage trading and whatever profit will be returned back to the account. These type of trading method require huge amount of fund scattered everywhere in different exchangers to take advantage of the spread during high volatility. So, it's like an investment option but with higher risk. Imagine if the owner run away with all the btc or on another scenario, they were not able to pay you back. You have to consider all these.
Unfortunately, "arbitrage trading" is also a common excuse used by ponzi scams to hide the true nature of their "investments". It was the excuse that Bitcoin-Trader used as well as the same excuse given by Pirate's ponzi.
Certain trading strategies involving arbitrage still work during market volatile time.
True, but "arbitrage" is also a perfect excuse for a ponzi scheme to cover the nature of their operations. And the fact that those traders that actually do perform arbitrage tend to keep the details of their operations secretive in order to maximize their returns doesn't help either. Personally I wouldn't trust any service that accepts investments if the source of the profits is simply attributed to "arbitrage".
I haven't seen anyone mention bitfinex. They (used to?) offer interest on btc and fiat within the exchange. Maybe that's not there now. dunno. The risk is that they just run off with your coins, but they've been looking pretty good for a long time now.
They still do. You can choose to offer liquidity to traders by providing funds for people to use to margin trade:
Our liquidity feature goes hand in hand with the margin trading feature described above. If you are not a trader and prefer safer investments, this feature is for you. Bitfinex allows you, using your deposit wallets, to provide liquidity in the form of Bitcoins and/or dollars to traders. You can enter offers with your own chosen terms (return rate, duration, and amount). When an offer is taken by a trader, the money in your wallet will be used to buy or sell Bitcoins, and a CFD (credit) will be opened. When the position expires (the trader closes his position), Bitcoins are bought or sold back and the money is returned to your wallet.
You are not exposed to exchange risk when you lend with Bitfinex. The exchange risk is taken on by the trader, and, in case his position loses money, he will cover the loss with funds in his trading wallet.
Link:
http://www.bitfinex.com/pages/howitworks#lending