Are There Large RDBMS Using Linux?

Jason Perlow of Linux Magazine writes:" With all of the recent computer press coverage of Amazon and Intel converting their web servers and other front end application servers to Linux, many of these stories neglect to mention that the back end systems these companies use still rely on commercial Unixes like Solaris, AIX and HPUX to host their RDBMSes (Oracle, DB2, Sybase, Informix) for their mission critical transactional applications and data mining. Are there any companies out there actively using Linux to host a mission-critical RDBMS ^? or looking to replace UNIX with Linux for this purpose?"