Which Ubuntu Version ?

I always forget how to find out, which version of the distribution I am using: here's the answer !

From the command line, lsb_release -a will print the distribution name as well as version number and uname -a the Kernel number.

In Gnome, you may get the information, going to System ==> About Ubuntu (this documentation will display the distribution version number).
Hard Info is a nice little utility tool, that will display plenty of useful information about you box, including the above.