Ubuntu 9.04 supports Ext4
Ubuntu 9.04 Alpha 3 already supports Ext4. This version of Ubuntu will be released in 29 April but until then the Ubuntu developers invite us to test the alpha/beta versions.
The most important change (in Ubuntu of course) is the latest EXT4 filesystem what will be as default in Ubuntu. Ext4 was merge in mainline code of kernel 2.6.28. Testers was impressed about Ext4 speed (some systems gain +30% speed at boot). Also Ext4 supports better unlimited directories and manage data types better. Ext4 can handle data up to 16 Terabytes and filesystems up to an Exabyte, deletion seems to be 20 times faster than Ext3 and fsck faster.
Good news for all linux users.