* RubyGems now promises to stay API compatible with whatever version of gems ships with the latest point release of Ruby 1.9. That means if RubyGems 1.8 ships with Ruby 1.9.3, the RubyGems 1.8 API will be preserved at a minimum until Ruby 1.9.4 comes out, which will be no sooner than 6-18 months from now.
* RubyGems has removed two deprecation warnings in 1.8.4 and 1.8.5 that account for virtually all deprecation warnings that were frustrating users.
* Bundler works out of the box on RubyGems 1.8, as does Rails 3. The next point release of Rails 2.3 will also support RubyGems 1.8. Evan Phoenix is a maintainer of both RubyGems and Bundler, and is taking the responsibility of cutting stable releases of RubyGems for the time being, which nearly guarantees there will be no further Bundler issues.
* Frequent point releases of RubyGems should hopefully be a thing of the past, because starting with RubyGems 1.9, there will be beta and release candidates running for a month long cycle before they get shipped as stable releases that get installed by gem update --system
You can find additional information here: http://blog.majesticseacreature.com/tag/rubygems