Generally, the term "soul mate" is something that people who watch too much Oprah & Doctor Phil use a lot. People who use this term in every day conversation are often so obsessive about finding their "soul mate", that they often overlook or dismiss people and/or relationships because they don't fit the mould of "soul mate" that they have formed in their minds. In the end, these people end up being bitter and unhappy because they can't find a person who lives up to their strict definition of soul mate. If the soul mate seeker finds someone that they deem worthy of "soul mate" status, that relationship is often strained because one or the other is trying too hard to live up to the hype of attaining or retaining soul mate status. Instead of being soul mates, they end up feeling like cell mates.
Just remember, if two people are exactly alike in every way and they agree on everything, then one of them isn't necessary.