Believe it or not, I have gotten virtually this exact question a number of times, which is really surprising given that this is a Christian evidences web site. Apparently a lot of people use this passage to teach about Christian dating and marriage!
First of all, the passage is definitely not discussing dating, as "dating" did not even exist in the first century. It is also not talking about marriage specifically. Paul is stating a principle rather than a rule in 2 Corinthians 6:14. Marriage is not mentioned in this passage. However, I believe it is a legitimate application of the principle to say that a Christian ought not to be involved in romantic or physical relationships with non-believers. If marriage is not a good example of being "unequally yoked," I do not know what is. It might be a bit more of a stretch to create a "rule" against dating a non-Christian from this passage as dating is not really a good example of being yoked. However, I do not believe it is gross misapplication. Anyone who uses this passage to teach that it is sinful to date a non-Christian is probably exaggerating. This is sloppy exegesis and smacks of legalism. Either that or they ought to explain carefully what they mean. Probably it would be better to make this advice rather than a rule. Besides, there are better passages to establish this spiritual advice than 2 Corinthians 6:14. I believe 1 Cor 7:39 is much better. This passage is about marriage. Paul is very specific and he is giving a command, not just advice. He says that those who are in the Lord can only marry those who are in the Lord.
It is my opinion that we marry those we date. For this reason it is a very bad idea for a Christian to date a non-Christian. However, this is not a direct commandment in the New Testament, so we ought to remember that this is very good spiritual advice, but not a commandment. Rather than saying it is a sin to date a non-Christian it is more accurate to say that to date a non-Christian is very unwise and is to put ourselves in a situation which is very likely to lead to sin.