Study after study has shown that the biggest causes of software project failure are over-optimistic scheduling and unstable requirements. I think the only reason team dynamics isn't in the #1 spot is that it's hard for an outsider to judge after the fact. In my experience, though, how well people work together is a lot more important than how smart they are individually: everyone in the engineering group of the first start-up I joined was very good at their job, but when you put us together, our IQs somehow canceled out.
I put together the profiles below to jump-start discussion in undergraduate project teams about the many ways in which someone can not contribute. If you have more to add, feel free to use the comment box :-)
Anna knows more about every subject than everyone else on the team put together—at least, she thinks she does. No matter what you say, she'll correct you; no matter what you know, she knows better. Annas are pretty easy to spot: if you keep track in team meetings of how often people interrupt one another, her score is usually higher than everyone else's put together.
Bao is a contrarian: no matter what anyone says, he'll take the opposite side. This is healthy in small doses, but when Bao does it, there's always another objection lurking behind the first half dozen.
Caitlin has so little confidence in her own ability (despite her good grades) that she won't make any decision, no matter how small, until she has checked with someone else. Everything has to be spelled out in detail for her so that there's no possibility of her getting anything wrong.
Frank believes that knowledge is power. He enjoys knowing things that other people don't—or to be more accurate, he enjoys it when people know he knows things they don't. Frank can actually make things work, but when asked how he did it, he'll grin and say, "Oh, I'm sure you can figure it out."
Hediyeh is quiet. Very quiet. She never speaks up in meetings, even when she knows that what other people are saying is wrong. She might contribute to the mailing list, but she's very sensitive to criticism, and will always back down rather than defending her point of view. Hediyeh isn't a troublemaker, but rather a lost opportunity.
Kenny is a hitchhiker. He has discovered that most people would rather shoulder some extra work than snitch, and he takes advantage of it at every turn. The frustrating thing is that he's so damn plausible when someone finally does confront him. "There have been mistakes on all sides," he says, or, "Well, I think you're nit-picking." The only way to deal with Kenny is to stand up to him: remember, if he's not doing his share, he's the bad guy, not you.
Melissa would easily have made the varsity procrastination team if she'd bothered to show up to tryouts. She means well—she really does feel bad about letting people down—but somehow something always comes up, and her tasks are never finished until the last possible moment. Of course, that means that everyone who is depending on her can't do their work until after the last possible moment...
Petra's favorite phrase is "why don't we". Why don't we write a GUI to help people edit the program's configuration files? Hey, why don't we invent our own little language for designing GUIs? Her energy and enthusiasm are hard to argue with, but argue you must. Otherwise, for every step you move forward, the project's goalposts will recede by two. This is called feature creep, and has ruined many projects that might otherwise have delivered something small, but useful.
Raj is rude. "It's just the way I talk," he says, "If you can't hack it, maybe you should find another team." His favorite phrase is, "That's stupid," and he uses obscenity as casually as minor characters in Tarantino films. His only redeeming grace is that he can't dissemble in front of the instructor as well as Kenny, so he's easier to get rid of.
Sergei is simply incompetent. He doesn't understand the problem, he hasn't bothered to master the tools and libraries he's supposed to be using, the code he checks in doesn't compile, and his thirty-second bug fixes introduce more problems than they solve. If he means well, try to re-partition the work so that he'll do less damage. If he doesn't, he should be treated like any other hitchhiker.