A lot of people want a close button for the Ubuntu notifications but unfortunately this won't happen - they don't want NotifyOSD to be customizable. But you can get notifications that have a close button by using the AWN Notifications Daemon.
We have a patched NotifyOSD that provides options to move the notifications to a different corner and such, but unfortunately it doesn't have an option to add a close button, however not many people are aware of the "Notification daemon" Avant Window Navigator applet. This applet has been around for a long time and it replaces NotifyOSD, providing some cool customizations (and of course, the notifications have a close button!): you can place the notifications anywhere on the screen, you can set it to display an icon in AWN that you can use to turn the notifications on/off with a click, set a sound for the notifications, specify custom colors for the notifications (or use the AWN theme colors), transparent (gradient factor) and more.
There's only one feature missing in the AWN Notification Daemon: there's no option to configure the font size. You can configure the font color, make the text body bold, but you can't change the font size and while the notifications look ok when using the default Ubuntu 10.10 font size (11 - but it looks ok with a font size of 10 too), it looks kind of small on my system with my preferred font size (9).
How to configure AWN Notification Daemon
To use the Avant Window Navigator Notification Daemon applet, simply install Avant Window Navigator and all the extra applets and add the "Notification Daemon" to the dock.
AWN Notification Daemon applet doesn't have a settings dialog, but you can tweak it using Gconf Editor. To customize it, press ALT + F2 and enter:
Then navigate to apps > awn-applet-notification-daemon (this is for the latest AWN from the AWN trunk PPA, it may be apps > avant-window-navigator > awn-applet-notification-daemon on older versions of Avant Window Navigator). Clicking a key will display its description at the bottom so you'll know how to tweak it. The most important key is: "kill_standard_daemon" - make sure this is enabled or else the AWN notifications won't work.
For instance, "override_x" is the horizontal position on the screen (for which I've used "1900" because my screen width is 1920 and I want the notifications to be displayed on the right), "override_y" is the vertical position (for which I've used "30" so the notification dialog is displayed in the top right corner) and "gradient_factor" is the transparency. That should be enough to get you started.
To customize the colors, uncheck the "use_theme" box, then specify a "text_colour" and "bg_colour" and so on.
An important feature you may want to turn on is "show_icon". This will display an icon on your Avant Window Navigator dock which you can then click to temporarily disable/enable the notifications.
How to test the notifications
When you configure the AWN Notification Daemon notifications, you'll want to see how they look. You can send a test notification by using "notify-send". To use it, install the following package:
sudo apt-get install libnotify-bin
Then copy/paste the following command in a terminal (this is the command I've used for the screenshot in this post, you can tweak it any way you want):
notify-send --icon="chromium" "Notification title" "Test notification - body text"
Want the regular NotifyOSD notifications back? Simply remove the applet from Avant Window Navigator.