Here's a nice e-mail from WordPress founder Matt Mullenweg. I like the personal approach that Wordpress / Automatic adopt.
Subject: WordPress 3.0 "Thelonious" available
"You've probably already seen the notice in your dashboards, so I'll keep this one short and sweet:
3.0 is faster, stabler, and more secure, so you can focus on what matters (your audience) and let the rest fade to the background.
Custom post types, MU merge, menu editor, Twenty Ten theme, over 1,200 bug fixes... there's so much to enjoy in this new release, we're really proud of it. It's the best WordPress yet, and available for a limited time for only free ninety nine. ;)
Tell your friends, help them upgrade, write new themes that use the new features, spread the good word.
http://ma.tt | http://wordpress.org
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If that was an indiscretion you'd rather forget, click below."
A nice touch.