The Java compiler developed for Eclipse is widely regarded as being one of the fastest and most capable in the industry, perhaps surpassing Sun's own javac. Due partly to its quality, and partly to its liberal open source license (which unlike GPL, lets it used by both open and closed source projects) it has found its way into a wide variety of applications. For example one major software vendor uses a modified version of the command line compiler to scan its code for I18N policy violations, and Apache has put it into their popular Tomcat web server to compile Java Server Pages.
Now JetBrains IDEA, which is putatively a competitor to Eclipse in the Java IDE realm, has announced plans to support this compiler in their commercial product. On the wiki page for new features in IDEA 6.0 (code named Demetra), one of the new Core Features is listed as "Support for the Eclipse Java compiler". With this feature, IDEA users would be able to enjoy super-fast compilations and superior diagnostics. Perhaps IDEA could even tie into the incremental compilation that gives the Eclipse compiler an advantage over ant-based alternatives. And since the Eclipse license requires any enhancements to be donated back as open source, it's possible that the wizards at JetBrains can make further improvements to the compiler that will benefit both the IDEA and Eclipse communities.