When starting with the PostMark mail server benchmark for the disk, there is not a large difference between Ubuntu 11.04 and 11.10 when using the default EXT4 file-system. An Intel Atom 330 and Core 2 Duo system each regressed slightly, but another Intel Atom 330 setup with a different system had marginally improved with Ubuntu 11.10. The three other systems had nearly identical results.
With FS-Mark there was not a huge difference in the EXT4 performance between Natty and Oneiric.
When running the FS-Mark test again, but without enforcing sync/fsync, the two Intel Atom systems, the AMD Phenom II X3 desktop, and the Core 2 Duo notebook heavily regress with Ubuntu 11.10 compared to Ubuntu 11.04. However, for the other more powerful systems (the AMD Opteron and Sandy Bridge) there are improvements with the latest release.