2 Cor. 6

Paul begins the chapter by talking about "our" hardships.  Presumably, this refers to him and his companions, for instance Timothy, but possibly others.  They have endured such difficulties as beatings, imprisonment, and hunger.

The second portion of the chapter deals with being "unequally yoked".  Paul advises Christians to not be "yoked" with unbelievers.

This is an odd statement and opens the question how far to take this.  Does this mean that Christians cannot be friends with or marry non-Christians?  Jesus ate with tax collectors and other "sinners".  Likewise, Paul's first epistle to the Corinthians discussed the effect of marriage between Christians and non-Christians.  If it were something to avoid entirely, he would have mentioned it.

Likewise, how an the Gospel spread if Christians all withdrew from the world and did not interact with the rest of society?  This would lead to a cult like mentality.

Rather, I think the passage refers to something common among Christians when interacting with  those of other faiths or non-faiths.  One's spiritual development can change the way other people interact with you.  One might have less in common with others.  

So, what exactly is a "yoke"?  I would think it refers to a long-term, formal partnership.  This could be marriage or perhaps even a business entity.  So, at the very least, the passage is a companion verse to Paul's prior instruction about marrying non-Christians - do not intentionally seek it out.  It is one thing to date/marry someone who is drawn to God, but still dealing with issues.  It is another thing to date/marry someone who is a committed Buddhist or virulent atheist.  

Even among Christians, unequal yokes could happen.  Consider the variance of worship practice among Catholics, Protestants, and other smaller groups like Adventists - what church to attend?  Or even, what day to attend church?

Likewise, for a business relationship, unequal yoking could involve a very different perspective on business ethics.  An extreme example is a Christian partnering up with mafia members for a business venture.  This would be bad.