I've posted the results of my 2.6.38/2.6.39 and 2.6.39/3.0 ext4 
scalability measurements and comparisons on a 48 core x86_64 server at:

http://free.linux.hp.com/~enw/ext4/2.6.39

http://free.linux.hp.com/~enw/ext4/3.0

The results include throughput and CPU efficiency graphs for five simple 
workloads, the raw data for same, and lockstats as well.

The data cover ext4 filesystems with and without journals.  For 
reference, ext3, xfs, and btrfs are included as well.

The 2.6.38/2.6.39 results mainly show the clear scalability benefit of 
making the mblk_io_submit mount option default behavior for ext4 
filesystems with journals - see the large_file_creates throughput plot.

In the way of more recent news, the 2.6.39/3.0 results indicate little 
change for ext4 either with or without journals.

Thanks,
Eric