To change the colour of the fast user switching applet, open the file to edit the colours with:

$ gedit .gtkrc-2.0

Then add these lines into the file (#FFFFFF for white):

style "modpanel" {
    fg[NORMAL] = "#FFFFFF"
}
widget "*PanelWidget*" style "modpanel"
widget "*PanelApplet*" style "modpanel"
widget "*fast-user-switch-applet*" style "modpanel"

Now run this code to reload the panels:

$ killall gnome-panel

(Taken from http://ubuntuforums.org/showpost.php?p=4315463&postcount=10)

Change desktop folder in Gnome

You need to edit the file ~/.config/user-dirs.dirs:

$ nano ~/.config/user-dirs.dirs

Modify the XDG_DESKTOP_DIR entry as needed. For instance:

XDG_DESKTOP_DIR="$HOME/.desktop"

Make Audacity work with Pulseaudio

Rename the file /usr/bin/audacity to /usr/bin/audacity.original:

$ sudo mv /usr/bin/audacity /usr/bin/audacity.original

Create a new /usr/bin/audacity file using:

$ sudo gedit /usr/bin/audacity

Then write the following lines into the file:

#!/bin/bash

padsp audacity.original "$@"

Save the file and make it executable:

$ sudo chmod +x /usr/bin/audacity

Enjoy! You can use the same trick with Skype and avidemux

Make Thunderbird the preferred email application for KDE

Modify the file $ ~/.kde/share/config/emaildefaults so it looks like this:

[Defaults]
Profile=Default

[PROFILE_Default]
EmailAddress=
EmailClient[$e]=thunderbird
FullName=First Last
Organization=
ReplyAddr=
ServerType=
TerminalClient=false

Change Icon Size in Konqueror

Under the [Settings] section in $ ~/.kde/share/config/konqiconviewrc modify the following parameter:

IconSize=48

Turn off the PC Speaker (Bell)

1. Uncomment the following line on /etc/inputrc:

   set bell-style visible

2. Restart

Custom Icons

A complete tutorial is available here