Anyone has been doing development for OS X has already taken a long hard look at Apple's latest operating system: Leopard 10.5. This release has a huge list of improvements that are specifically targeted at developers.
While there is a controversy about whether this release is truly valuable for the consumer, there can be no argument that it is of large value to the developer community. Because of this there is an equally large question of whether or not we, as developers, should take the plunge and start developing for Leopard right away.
The answer to that question, as always, is not as simple as yes or no. First, you have to look at where you are now. Are you developing something completely new? Are you building a new version of an existing application or will this next release be a minor enhancement?
Whether you have an existing application that you want to upgrade to Leopard or you are developing a new application, the target audience is the most important aspect.
If you are looking to target educational markets, you should probably not be looking at Leopard—and possibly not even Tiger. This market segment is considered slow to upgrade their hardware, operating systems, and software.
If you want to get into the educational market, you might want to take a survey of the campuses around you. See what version of OS X they are running on. Do not be surprised when they are running on some very old versions or (even worse) a mix of versions.