As Ubuntu and Gnome gets modernized, Xfce begins to look like a natural replacement for the "conservative Gnome" that many are used to. And even if the modern desktops are nice, some people will prefer the old ways. But can you simply switch from Gnome 2 to Xfce4 or are there things to consider? I am asking this as a single question, but it can obviously be broken down into many:
- Can I still use the app-indicators that I'm used to?
- Can I still use Gnome panel applets?
- Is it possible to use Compiz with the plugins I've been using?
- Can I use custom launchers and docks like I can in Gnome 2?
- Can I use the same themes, icons, etc?
- Is it ok to just install xubuntu-desktop on my Ubuntu install, or should I install Xubuntu from scratch?
Since I haven't done this, I don't know what questions to ask. So even if I haven't asked them, please do answer them if there are important things to consider.
Xfce4-panel can use Gnome panel applets if you install the package xfce4-xfapplet-plugin. Not all applets will make as much sense though. The session applet, for instance, will attempt to log you out of Gnome 2, which isn't running, so it will do nothing. The same goes for applets that handle the screensaver and other such DE-specific things. In those cases, the xfce4-panel will have its own plugins that provides these features.
App-indicators are based on DBus, which means they can be used on any desktop environment that supports it. This is one of the big benefits of indicators. They'll work well on KDE, Gnome Shell, Unity, LXDE, Xfce or any other environment. I do believe that there is a native xfce4 plugin to display indicators, but in any case, you'll be able to use the Gnome panel applet just as you did in Gnome.
Using a custom dock like Docky or AWN, should not be a problem at all. I haven't tried it.
I see no reason why you shouldn't be able to use Compiz and all its plugins. I haven't tried that either. But I have used Xfce4-panel with Compiz, and that works well.
You can use the same icons, but window decorators will be different. Perhaps if you use Compiz, you can still use the other themes, but I don't know.
You can just install xubuntu-desktop, except for a single conflict: the notification system. You'll be told that ubuntu-desktop needs to be uninstalled, but that will not uninstall all your software. However, since both Gnome and Xfce provides tools to handle screensavers, sessions, etc, it might be cleaner to do a fresh install.
As I did this about a week ago, here is an updated answer for 12.10:
xfce4-xfapplet-plugin is no longer available in Ubuntu repositories, and wouldn't really be useful even if it was, because xfce is currently based on gtk2 and so xfapplet would only be able to show gtk2 gnome-panel applets, none of which are available in the Ubuntu repositories. So basically, no, you cannot use gnome-panel applets in Xubuntu any more, not without compiling loads of software yourself.
likewise, app-indicators are barely supported for the same reason. Anything which goes through indicator-application will work eg weather, cpufreq, skype. The sound indicator still has a gtk2 port. None of the really important stuff (datetime, session, messaging, printers, bluetooth) are still maintained as gtk2 ports, so these won't be available in Xubuntu 12.10. Some of them have equivalent plugins in xfce, some don't. You'll rely much more on the old gnome2-style notification icons which don't work at all with multimonitor.
xfce supplies different default applications. The main thing missing from these is Ubuntu One integration, especially in the file manager and music apps.
compiz still works just the same as it always did, although 0.9 is somewhat less stable and slower than 0.8. If you want to configure the compiz window decorations you need to use gnome-tweak-tool. All the plugins like desktop wall work just the same with xfce4-panel as they did with gnome-panel. You will need to configure compiz from scratch because the defaults have been totally changed to accommodate Unity.
xfce supports gtk2 themes, though if you want all your gtk applications to look decent you need to find a gtk theme that supports both gtk2 and gtk3, which dramatically limits your choices. Basically light-themes are still the best. The icon packs (ubuntu-mono-light/dark) work fine.
Whether to install xubuntu-desktop or ubuntu-desktop? If you install them both you will get two text editors, two video players, two file managers etc etc. which is not a good thing at all when you have a "start menu" style desktop. But as noted above, the xubuntu-desktop apps really aren't as good as their gnome counterparts. There are a few other minor irritations eg the default Xubuntu screensaver isn't smart enough to know not to activate when you are watching a video or playing a fullscreen game. So if you only want a traditional panel type desktop you are probably better off installing ubuntu-desktop and then installing xfce4-panel and dependencies, and not the full xubuntu-desktop. That's my recommendation anyway.