From some of the posts in this thread, apparently it is not okay to sleep with a man you have never seen before but it is okay to sleep with a man you have seen once before.
Okay that was the punch line. Now, I dont agree with the assumption that the guy you have chosen for yourself would be better than who your parents would choose for you. The guy you know from somewhere - be that school/college, work, otherwise, might not turn out to be the person you think he is. When dating and courting, people tend to be at the best of their behavior, and many pretend to be the best people on the planet. Someone who apparently is all neat looking, could have serious psychological issues that you are not aware of. My point is, in majority of cases marriage is a chance. From religious point of view, I am not an expert but I believe it has more to do with your destiny that Allah has written for you. You just can never be sure. Ideally, you would certainly be more comfortable with someone you know
Your parents, on the other hand, will keep many things in mind while choosing someone for you. Their family background, education, job, future - any parent will want to be sure about that person before they agree on marrying their daughter to them. Then again, its a chance that they take, but based on a well-worked risk management approach. And again, you can never be sure. In good old days, it was normally the parents' job to arrange such deals, and majority worked out very well.
Having said all, yes one should get to see (ideally in a short meeting) their partner-to-be to ensure that they arent hideous or otherwise repellent.
Zabardast and Agree fully.