PB Web Dev Blog
Another version of Joomla has been released to patch a few issues with version 1.5.16. If you haven't upgraded to 1.5.16 then don't worry about it. Skip it and move straight on to 1.5.17. I personally had issues when testing the upgrades over the weekend and had to revert back to Joomla 1.5.15 to get things working again.