Whenever a new version of WordPress comes out (as just WordPress 2.6 did), it is somewhat of a pain to upgrade it.
But not for me anymore, because I have created a small (and simple) script some versions ago which I would like to share with you.
$ cat upgrade_wordpress.sh
mv www wordpress
tar --overwrite -xzf latest.tar.gz
mv wordpress www
www is my document root and the script sits outside of it. It downloads the most recent version, extracts it while overwriting the already existing files. The script doesn't contain anything extra-ordinary, but makes upgrading real easy.
Of course this script is only useful if you have ssh access to your web server, but if you do that script might ease the (almost too frequent) pain of upgrading WordPress.