Official support for Joomla 1.0 will end in 281 days. That announcement was made by Wilco Jansen on joomla.org. July 22, 2009 will be the two year anniversary of the first Joomla 1.5 release, and it seems an appropriate day to move forward.
I’m sure this is a popular decision within the Joomla team and also with third-party devs who can concentrate on developing for just one version. Mathias from JoomlaTools was one person pushing for this to happen.
It’s probably less popular with the thousands of people who still use Joomla 1.0. However, there’s no reason to get worried. Personally I’ve made so many hacks and modifications to Alledia.com that we’ll probably never upgrade. We build all our new websites with 1.5, but see no reason to upgrade existing installations. You can expect several Joomla developers to fill the gap of providing 1.0 support while the core team keeps pushing ahead.