Big day today - Aperture 3 is out! 

I'm a Lightroom user, but I'm willing to give it a try, considering the bazillion changes they made. The most notable improvements are:

• Adjustment Brush - you know, the one we've been enjoying in Lightroom for a while now
• Presets - finally
• Stills, Video, and Audio management - sounds incredibly useful with the fact that video on DSLR's are becoming a new standard
• Faces and Places - the same nifty stuff we've seen in iPhoto
• Slideshows - I think we all know what they are
• Photo Books - new sizes and now with the ability to send your books out to professional photo labs via plug-ins (now that's a welcome new feature!)
• Printing - lots of new printing options
• 64-bit - Under-the-hood improvement that should help with speed and access to RAM

Check out all of the improvements here.