If I filed as single and have a refund sent to a joint account with my name and someone else's name on the account, will that create a problem for direct deposit?

No, as long as your name is on the account, you should get your direct deposit. However, you can check with your bank to make sure. 

Speed, security, and convenience. By e-filing and choosing direct deposit, the IRS expects to issue 9 out of 10 refunds within 21 days, as opposed to 4-6 weeks for a check in the mail.

With a direct-deposited refund, you don't need to worry about your check getting lost in the mail, nor do have to go to the bank to deposit or cash it.

You can even split a direct-deposited refund into 2 or 3 different accounts (unless you're using the optional Refund Processing Service to pay your TurboTax fees).

Please note that due to IRS regulations, you cannot direct-deposit your refund into foreign accounts – only domestic accounts located in the United States.

Also, the IRS won't let you deposit more than 3 refunds into the same bank account during a given year. If a bank account has already received 3 direct-deposits from the IRS, any additional deposit requests will instead be mailed out as refund checks.