The main pitfall is libel, in case your story clearly maps to an individual. If I wrote a story in first-person, used the real name of my college, then cast the a supporting character as "my closest friend," who "was an electrical-engineering major," then went on to describe something "we did" that could potentially harm his career... I can be sued. Even if the story is presumed to be fiction. If the story is in fact true to the letter, then by labeling it "fiction" we've violated a fundamental media ethic, which is to label all content truthfully and accurately and to keep different types of content visually separate. The worse violations I see are ads posing as reviews and opinion posing as news, but I digress....(ever clicked on a link or a download mirror that was a trick to peel an ad-click out of you? Did you trust the site afterward?)
Some of my favorite writers based nearly ALL of their work on personal experience. Hemingway simply tapped out as many words as he could about his adventures, some exaggerated, some not. Since he was THE ERNEST HEMINGWAY, most of his "typing" ended up in periodicals, collected into volumes and published as books.
On a less abstract side, F. Scott Fitzgerald used an extremely popular technique that (for me) is the only way I can write "honest, authentic" fiction. The main character in his stories is HIM - albeit a fictionalized version of him. The other characters are based on people he KNEW.
Woody Allen is another example, in nearly all his plays and scripts, the main character is a lightly fictionalized version of himself, in his movies he plays the main character for this exact reason to great effect.
I find more pitfalls in writing 100 percent fictional characters. How can there be any authentic dialogue or action with someone who isn't even BASED on ANYONE or ANYTHING KNOWN to the writer? Perhaps some have better imaginations than me.
The important thing is that if the character IS essentially your best-friend from college, then change the college, the character's name, the location...as much as you need so if/when you tell a libelous anecdote within the story, it's essentially untraceable. Minimization of harm is the key concept & ethic. A good college story isn't going to be about going to class on time, getting good grades, studying and staying sober. Ideally, we'd like our friend's boss and his wife to think that is all he did in school. The 18 year old version of a character is going to be vastly different from his 40 year old self. That goes triple for self-based characters. Ask the teenage me, the mid-20s me and ME (the real me) the same question and you are likely to get vastly different answers. Consider their differences, strengths and foibles when you set a fictional character's age that is based in reality (on some level).
"Art (naturally) reflects life," I think most fiction writers base characters and relationships on real ones whether they know it or not. The important thing is re-name, re-stage and change the time period or ages of the characters.
Carrying the "This piece is a work of fiction. Any resemblance ..." statement is always good, especially if a character is CLEARLY an ex, or an old boss or ... you get the idea.