Bitcoin is still experimental and some of the business are not using good practices. Also, banks are unclear of the regulations and may close accounts of companies rather than take the risk of maintain the account. There is also risk of regulation.
-An online site generally has control of the “private key” to your bitcoins and has control of your other funds. they may go out of business, they may get hacked and have no way to pay you back, or they may simply steal your funds
-The accounts are generally not insured.
-The banks could freeze or close the accounts making it difficult to recover funds.
-Regulators could take some type of enforcement action and freeze accounts or shut them down.
-Your computer could be hacked and the log-in information stolen. Most sites will not cover this type of loss. many sites use “2-factor” login. this means you can’t log in with just a username/password. A hardware device, message to your phone, or an e-mail will have the additional information needed to log in. For instance, a hacker would need to gain access to the username. password, and your cell phone to steal the wallet.
-Some sites have poor support and it may take weeks to get an answer if an issue arises.