My only issue with it is I don't like the notification window that lets you know you have new emails, I would much rather have the native notifications from Ubuntu.
This is how that can be done:
First you need the the libnotify package which is easy in Ubuntu (sudo apt-get install libnotify) now you can make your own notifications by typing
notify-send "Hello World"
If you now go into the CheckGmail preferences and set the pop up time to 0 secs to and put the following into "Command to execute on new mail":
if [ %m = 1 ] ; then mess="Message"; else mess="Messages"; fi; notify-send "You have %m New $mess" -i ~/bin/gmail.png
The %m is a variable of how many emails you have just recived so a lot of the code is determining whether to use the plural or not. The last bit is a link to a Gmail icon.
via Tom Hare's Blog