Here’s the one-step upgrading I did for upgrading from 2.8-Beta2 to 2.8-RC1.

~$ ./update
U    /u/h67959/home/blog/wp-includes/version.php
U    /u/h67959/home/blog/wp-includes/functions.php
U    /u/h67959/home/blog/wp-includes/link-template.php
U    /u/h67959/home/blog/wp-includes/script-loader.php
D    /u/h67959/home/blog/wp-admin/cache-manifest.php
U    /u/h67959/home/blog/wp-admin/wp-admin.css
U    /u/h67959/home/blog/wp-admin/includes/plugin-install.php
U    /u/h67959/home/blog/wp-admin/includes/post.php
U    /u/h67959/home/blog/wp-admin/includes/template.php
U    /u/h67959/home/blog/wp-admin/js/common.dev.js
U    /u/h67959/home/blog/wp-admin/js/common.js
U    /u/h67959/home/blog/wp-admin/css/press-this.css
U    /u/h67959/home/blog/wp-admin/css/colors-fresh.css
U    /u/h67959/home/blog/wp-admin/css/colors-classic.css
U    /u/h67959/home/blog/wp-admin/themes.php

Fetching external item into '/u/h67959/home/blog/wp-content/plugins/akismet'
Updated external to revision 124424.

Updated to revision 11542.
At revision 948.
~$

Yes, one line. I’ll post another tips on how to upgrade from 2.7.1 to 2.8 with one command (+ one upgrade.php, IIRC) once it’s released (sometime today?). HA HA HA forget that. I just remembered there’s one-click update since 2.7. I still trust svn than some-php-lol-unzip-and-do-ftp-upload which I find unreliable depends on your webhost.