The march to a stable Joomla 1.5 quickened earlier this month with the release of RC3. Here's some helpful links about RC3.
Read the official news: http://www.joomla.org/content/view/3994/1/
Instructions for upgrading from RC2 to RC3: http://forum.joomla.org/index.php?board=430.0
Discuss Joomla 1.5 on our forum: http://www.joomlashack.com/community/index.php/topic,6544.0.html
Joomla 1.5 installation guide: http://www.joomla.org/component/option,com_jd-wp/Itemid,105/p,419/
If you're curious when Joomla 1.5 is going to "released" and "finished," better check out this perspective piece by one of Joomla's core team members and developers. Needless to say, RC3 is not the last of the RCs, as Joomla's developers believe in the "release early, release often" philosophy of open source development.