The reference you link to, wikicu, appears to be largely taken from Obama's own autobiographies written later, or his campaign materials, which contain many statements whose historical accuracy is highly dubious. There is absolutely not one direct quotation in the wikicu article from a Columbia classmate recalling Obama's days as a student there.
The only evidence vaguely suggesting he was a student there was an article the campus publication, "The Sundial," written under Obama's byline.
I'm well aware or Root's story and have quoted it myself. But we do have to realize that Root and his crowd, and Obama and whomever he associated with would not likely have had anything in common.
Supposedly this Professor Michael Baron remembered Obama during an interview by NBC News. (source) Also the NYT reported:
One person who did remember Mr. Obama was Michael L. Baron, who taught a senior seminar on international politics and American policy. Mr. Baron, now president of an electronics company in Florida, said he was Mr. Obamas adviser on the senior thesis for that course. Mr. Baron, who later wrote Mr. Obama a recommendation for Harvard Law School, gave him an A in the course.Right now it's still way too much for me to believe that Obama never attended Columbia.
ML/NJ