I recently did a clean upgrade to 8.04, preserving only my home directory, and noticed that my XFCE desktop menu's Settings sub-menu was abridged. In 7.04, my Settings sub-menu contained an entry for "Settings Manager" as well as all entries of the individual buttons you find therein (e.g. "User Interface, "Window Manager", "Window Manager Tweaks", etc). I have no idea why the duplicate entries were there, but I appreciated the convenience. After upgrading to 8.04, these entries no longer appeared, along with the "Settings Manager" entry.
I found the master menu.xml file in: /etc/xdg/xfce4/desktop/menu.xml and diffed this against my local menu file in ~/.config/xfce4/desktop. Sure enough, there were a few differences. The master file, which is used as a template when you create a new user, contains:
<menu name="Settings" icon="gnome-settings">
<app name="Settings Manager" cmd="xfce-setting-show" snotify="true" icon="gnome-settings"/>
</menu>
<separator/>
<!--
The next line includes the autogenerated menu at the current level. If
you want, you can put this in its own submenu.
-->
<include type="system" style="simple" unique="true"/>
The equivalent area in my personal menu.xml contained only:
<include type="system" style="simple" unique="true" legacy="true"/>
The directives in the template file manually insert a link to "Settings Manager"; however, it seems that in 7.10, XFCE automatically inserted menu links for all of the configuration programs and "Settings Manager" by scanning the system for .desktop shortcut files. I have no idea what stopped it from doing so after the upgrade, but I remember having a similar issue back when I went from 7.04 to 7.10.
Copying the relevant section in the template file into my personal menu.xml did not restore all of the extra configuration links I had in 7.10, but it did get the "Settings Manager" back (and through that, I have access to everything else).