Jonathan Adler's post below highlights the seemingly surprising fact that the conservative College Republicans are the largest and possibly most unified student group at the generally very liberal University of Californiat at Berkeley. This fact, however, is not as strange as it seems.
Basic collective action theory, as outlined in Mancur Olson's classic work The Logic of Collective Action (well summarized here), shows that it is easier to mobilize a small group than a larger one. The bigger the group, the more likely it is that some members will fail to contribute to the achievement of its common goals and instead free-ride on the efforts of others. In a small group, bu contrast, members know that if they fail to contribute, it is not likely that anyone else will pick up the slack. Moreover, it is usually easier and cheaper to organize and assemble a smaller number of people than a larger number. For this reason, it is likely that a much higher percentage of the conservative students at Berkeley take an active part in conservative organizations than liberal students who actively contribute to liberal ones.
It is also easy to understand why the conservative students tend to be unified in one organization (in this case the College Republicans), while the liberal ones are "splintered" into many factions, as the Wall Street Journal article quoted by Jonathan notes. Precisely because they are so heavily outnumbered, Berkeley conservatives know that they are unlikely to achieve much in the face of overwhelming liberal dominance if they fail to cooperate; being a beleaguered minority is conducive to unity in a way that majority status often is not.
I saw the same logic at work when I was a student at Yale Law School, where right of center students (including both conservatives and libertarians) were probably no more than 10% of the student body. Yet the Federalist Society was one of the largest student groups, and certainly one of the most active. We few YLS right-wingers knew that if we didn't work to promote our cause, nobody else at the Law School would either. And the overwhelming predominance of liberal and leftist students gave us a stronger incentive to put aside our differences than would otherwise have been the case. Indeed, the YLS Fed Soc at that time (1997-2000) included a variety of libertarians, social conservatives, neoconservatives, and even a few centrist Democrats. These disparate factions were willing to work together in large part because of the fact that we were so heavily outnumbered on campus by the political left. During the impeachment of President Clinton, which occurred during my second year at Yale, I wasn't shy about saying that I was opposed to efforts to remove him from office. Yet no one in the YLS Fed Soc seemed to mind my apostasy, despite the fact that one of the organization's leaders had spent the previous summer working for Ken Starr's independent counsel office.
Liberal YLS students, by contrast, had few such incentives to avoid factionalism and free-riding and as a result were split up among numerous groups focusing on single issues or (less commonly) on one particular narrow type of left-wing ideology.
When will we know that liberal dominance on campus has truly ended? When conservative and libertarian students engage in as much free-riding and factional in-fighting as liberal ones do today:)!