Many law firms have banks of precedents to refer to for research, memos, pleadings and so on. So far there has not been any substantive effort to consolidate the work online, like on Wikipedia. Such an effort would devastate the traditional legal publishing community but would be a valuable resource to lawyers and laypeople alike.
At the moment, there is not a strong incentive to share legal precedents between firms and make it publicly available, even though we would all benefit from doing so.
However, the trend is moving towards a consolidated bank of precedents. More and more lawyers and law firms are blogging about current legal issues and cases.
Part of the reason for this development is the change in the underlying information substructure. As Richard Susskind remarks, we are moving from a print-based society to an internet-based society. And since law is an information based profession, a change in the way information is disseminated alters the profession as a whole.
The legal community should look towards other industries that are information based for examples on how best to respond. For example, the New York Times released a fantastic report on how they plan to innovate in an internet-based society.