[activepeanut]

One downside worth mentioning is that you can't read the full description of each available updates, like you can when you click on an item in the GUI version.

[jasomill]

    softwareupdate -d -a

downloads all updates to /Library/Updates. For each update, you get a .pkg file to install and a metadata file that includes this description.

[_pdeschen]

Indeed. Moreover, I only want to update my jdk when Im ready and have some free time to repair my jdk 1.5 symlinks once the update completes.