You can hop directly to the original mailing list post here: http://lists.openwall.net/linux-ext4/2010/01/04/8 (the entire thread is a good read for anyone curious about file system benchmarking).
Why is that link pointing to google in first place??
I wouldn't really call this "bashing" dbench. He is simply saying that it is a good tool, especially with regard to exercising the VFS layer, but is not complete enough to do everything they could ask for (like emulating their customer workloads). I read it more as a warning to see what it actually does for you and not get caught up in the hype.