Answer:
There are both Advantages and disadvantages to this, this answer will discuss both.
People in Co-Ed tend to have a broader outlook on life as they have been exposed to both male and female views on life and organisation etc.
People in Co-Ed Tend to know better how to react around a member of the opposite sex, a couple of weeks ago i was at a science and engineering competition and there were some boys from a single sex school when some girls walked up to their stand, they were so nervous it is unimaginable! Unlike how the previous answer suggested i think that this a contributing factor to teen pregnancies as gentlemen that have never been exposed to members of the opposite sex instantly make assumptions (as some girls were telling me just the other day!) But do not take that as red as it's just my opinion.
Co-Ed Students however do get very distracted by members of the opposite sex, and it is possible that their education suffers because of this. However this also applies to gay or bisexual students in single sex schools.
My experience of students from single sex schools is that they tend to be out of touch with life and very focused on their education but as soon as they are out of full time education they tend to stay out of touch with life and do not have the skills necessary to converse and relate with the opposite sex.