Big update from Apple - they made a trial version of Aperture available to everyone! Is this a move to compete with Adobe Photoshop Lightroom? I think so. Lightroom is offered for free (since it's still in beta), and this is the only way for Apple to attract more photographers to use their product.
My initial impressions - Lightroom is very simple to use and light on the machine. Aperture requires more processing power. Aperture's interface seems to have been designed for advanced photographers. Meanwhile, Lightroom has the simple menus like presets to fix white balance, etc. I will find time and post my comments on Lightroom's latest version (beta 4.1).
Apple also posted an update to Aperture (version 1.5.1 now).
Aperture -> www.apple.com/aperture
Lightroom -> labs.adobe.com