The notes on Joomla.org points out that the version of the WYSIWYG editor TinyMCE received an important upgrade in this release, which reminded us to remind you that if you aren’t using WYSIWYGPro, you’re mising out on the best editor available for Joomla 1.5.
Nonetheless, be sure to do your updates early and often, as there are likely bad people out there trying to hack your Joomla site. You can also check out SecureJoomla, which will add another layer of protection on top of the great work by the Joomla Project guys.