For those looking to build plug-ins (applications or platform extensions) for the Notes 8.5 client platform, the Expeditor Toolkit / Notes getting started article has been updated. It is on the Expeditor Wiki at http://www-10.lotus.com/ldd/lewiki.nsf/dx/12092008063131PMJMI2M6.htm
Since Notes 8.5 is built on top of Expeditor 6.2, the Expeditor Wiki should be a good resources for those looking into or working with plug-ins, specifically Eclipse plug-ins, and the Expeditor portions of the Notes platform - http://www-10.lotus.com/ldd/lewiki.nsf/