I installed only the Hibernate support from JBoss Tools, since it's all that I need, but when I started Eclipse for the first time after install, I got the following error from the org.jboss.tools.common.model:

eclipse.buildId=I20090611-1540
java.version=1.6.0_16
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86, WS=win32, NL=pt_BR
Framework arguments: -product org.eclipse.epp.package.reporting.product
Command-line arguments: -os win32 -ws win32 -arch x86 -product org.eclipse.epp.package.reporting.product

Info
Thu Aug 20 16:01:19 BRT 2009
ClassLoaderUtil:activate: Cannot find required plugin org.jboss.tools.jsf.ui

Besides not being declared in the plugin descriptor (otherwise I wouln't have been able to install it), a "model" package depending on a UI package smells like cyclic dependency...