Nightly builds are direct builds from SVN/CVS and are provided as-is with no guarantees. Be advised that while there is no prior proof, if this build sets fire to your computer, you were sufficiently warned!
Any suggestions/issues should be posted on the relevant product forums and should clearly indicate that you are using a nightly build - ideally stating the specific build ID (timestamp and Hudson build number) so as to better identify which bits you used. Please take care in making sure that your issue hasn't already been fixed in a newer Nightly build when posting on forums or opening new JIRA issues.
First time installing JBoss Tools? See http://www.jboss.org/tools/download/installation.