Terminal tries to reduce the number of running instances by establishing a D-BUS service that handles all terminal windows. The message above tells you that Terminal wasn't able to connect to the D-BUS session message daemon and register a service. This is just a warning, you can use the terminal without the D-BUS service feature as well.

To start the D-BUS session message daemon when you login to your X session, either modify your xinitrc file and change the line xfce4-session to dbus-launch xfce4-session or use dbus-launch startxfce4 to start Xfce instead. If you don't use Xfce, please look at the documentation of your desktop environment on how to enable the D-BUS session daemon.

This problem is actually a bug in vte, the terminal widget used by Terminal. A patch for vte that fixes the problem is available here (this patch was created with version 0.11.11 of vte, it may not work with other versions). Thanks to Auke Kok for this patch.

You can customize the main menubar and the right-click popup menu by editing the file Terminal/Terminal.ui. Create a copy of this file before you actually start editing it. For example, say you installed Terminal in /usr/local, then you would perform the following steps:

$ mkdir -p ~/.local/share/Terminal
$ cd ~/.local/share/Terminal
$ cp /usr/local/share/Terminal/Terminal.ui .

Now you can safely edit the file ~/.local/share/Terminal/Terminal.ui to customize the menus. See the GtkUIManager documentation for details on the file format. The changes will only be visible in new terminal windows.

If you choose to customize your menus this way, you'll have to take care to sync your customized Terminal.ui file when you upgrade to a newer Terminal release to keep up with user interface changes and additions.