Why is the next release of Eclipse called 3.0 rather than 2.2?
For the next Eclipse release we are planning both consolidation and major new functionality. Some of the changes that we are considering would require us to break compatibility with existing plug-ins. Incrementing the minor version number from "2.1" to "2.2" suggested that all existing 2.* plug-ins would run on the new release without change. Changing the major version number from "2" to "3" suggests that existing 2.* plug-ins do not work with the new release, and would need to be ported to 3.0. This gives the development team more maneuvering room and more accurately sets expectations.

Does this mean that Eclipse APIs will be changing in incompatible ways?
Yes. Some of the Eclipse APIs will likely change in ways that will require rewriting portions of existing plug-ins written to the 2.* APIs. Most of the Eclipse APIs will remain the same.

Does this mean that plug-ins based on Eclipse 2.0 and 2.1 will not work in 3.0?
Yes. The changes to the Eclipse APIs in 3.0 will mean that existing 2.1 (and 2.0) plug-ins will not work with Eclipse 3.0. Developers of 2.1 plug-ins will need to port them to 3.0, and ship new versions of their plug-ins.