This absolutely backs up my own findings-<p>I've been working to decrease the mailserver backup times.
Our Zimbra mailstore was taking over 8 hours to backup; I started compressing teh files before writing them to disk and it made a huge difference. I was able to bring the total time down to 3 hours.<p>I attributed this to two factors- The first was, as the article mentions, that the machine has so much CPU when compared to disk, that the smaller data-transfer helped more than the CPU overhead hurt. 
I found that this is true for gzip, but bzip2 slowed it down. An implementation of parallel-bzip I found online spreads the bzip cost over multiple cores, reduced this further, however. This leads me to believe that something closer to the OS, which would adjust the compression level dynamically with CPU load, may be a wonderful product.<p>The second factor was that the compressed files were in tarballs, so didn't create nearly as many files. Zimbra creates one file per message (a maildir like format), so this means hundreds of thousands of files need to be created and sized on the disk. In the archives, however, I am able to store just a few, large files, reducing the overhead of individually creating each message.