Ubuntu is a good distribution, but its default colour theme is pretty awful. Ubuntu brown begone! And take the cuddling lovies with you, too!

The following description applies to Gnome 2.10:

Grub splash screen

sudo vim /boot/grub/menu.lst

Find the line that reads # defoptions=, and delete the word splash

sudo update-grub

OK, so this is nothing to do with Gnome, but it's part of getting rid of the Ubuntu "branding"

Gnome login splash screen

System Tools->Configuration Editor (gconf-editor)

apps/gnome-session/options

splash_image

splash/your_preferred_image.png

The path is relative to /usr/share/pixmaps, though I believe that you can specify an absolute path if you wish. You might like to download a splash screen from art.gnome.org

System->Preferences->Sound

Sounds

Don't play system sounds

Begone the twiddly little candy-music, too

Splash screen background colour

System->Admin->Login Screen Setup (gdmsetup)

Standard Greeter, Background Color

Window theme

You can either choose one of the themes on offer, or mix and match.

System->Preferences->Theme

Theme Details lets you separately choose themes for the Controls (the top window-bar), the Window Border, and the Icons.

To download and install a theme, go to art.gnome.org. Download a theme in the form of a tar.gz file, then you can install it from the Theme manager.

Desktop background

System->Preferences->Desktop Background, or right-click on the desktop background and choose Change Desktop Background

Add Wallpaper

Choose a picture Style: Fill Screen

Make your panels disappear properly

Right-click on the panel, Properties

Autohide

gconf-editor (System Tools->Configuration Editor)

apps/panel/toplevels/bottom_panel_screen0/auto_hide_size

1

If you only have 1024x768 pixels, you don't want to lose too many of them to the panels.

Gnome footprint for your main menu icon

gconf-editor (System Tools->Configuration Editor)

apps/panel/objects

Find the object_n that has the smallest value for "position" use_custom_icon custom_icon

your_preferred_icon_name

The path is relative to /usr/share/pixmap, or you can use a full path

Gnome Terminal

Right-click in the terminal, Edit Current Profile

Effects

Transparent background - Set the slider bar to about half way, or, if you choose an appropriately monochromatic background for your desktop, set it fully transparent

Colors

The above change will make your "ls" colours pretty invisible, so you can darken them up using the Colors tab. Select the "Custom" built-in scheme, then click on each colour in turn. Lower the "Value" setting to about 65% for the lighter colours, and 40% for the darker ones.