The widely known licenses conforming to the Open Source Definition have well-established interpretive traditions. Developers (and, to the extent they care, users) know what they imply, and have a reasonable take on the risks and tradeoffs they involve. Therefore, use one of the standard licenses carried on the OSI site if at all possible.

If you must write your own license, be sure to have it certified by OSI. This will avoid a lot of argument and overhead. Unless you've been through it, you have no idea how nasty a licensing flamewar can get; people become passionate because the licenses are regarded as almost-sacred covenants touching the core values of the open-source community.

Furthermore, the presence of an established interpretive tradition may prove important if your license is ever tested in court. At time of writing (mid-2003) there is no case law either supporting or invalidating any open-source license. However, it is a legal doctrine (at least in the United States, and probably in other common-law countries such as England and the rest of the British Commonwealth) that courts are supposed to interpret licenses and contracts according to the expectations and practices of the community in which they originated. There is thus good reason to hope that open-source community practice will be determinative when the court system finally has to cope.