Aaron Patterson has a solution for native Windows RubyGems that support both Ruby 1.8 and 1.9 at the same time: fat binary gems. Fat gems contain the shared libraries for both targets and determine at run-time which one to load.
Luis Lavena from rake-compiler is already working on integrating Aaron's changes and has published a beta version of rake-compiler. For a simple example on fat gems, take a look at Aaron's demo on GitHub.
Fat binary gems seem to work "similar to providing JRuby and Ruby support in the same gem by just publishing and loading the jar file extension when in JRuby", as Charles Nutter commented on Aaraon's blog.
Regarding JRuby and RubyGems, the recently launched is it JRuby shows the status of JRuby compatibility for popular gems in the same fashion as is it Ruby 1.9 does.
RubyGems 1.3.2 introduced plugins, and in the past few weeks, some new plugins have emerged: Gabriel Horner shows how to write plugins using a gem grep plugin as an example and Adam Sanderson wrote an open plugin that simply opens a gem in the default editor.
