Leopard for me

As culled from the New Features page.

Things I like:

• Google Mapping of Address Book addresses
• Automator
• Automator UI improvements
• UI recording and playback
• New actions
• Dashboard web clipping
• Stacks (esp. Downloads stacking)
• Icon preview and Quick Look
  
• Improved iCal interface
• iChat invisibility
• Mail.app
• RSS feed reading
• Auto-detection of data
• PDF manipulation and markup in Preview (I have programs that do this, but it would be nice for them to all be in the same place)
• Spaces
• Spotlight
• Calculations
• Advanced syntax
• Time Machine

Things I don't like and/or am scared about:

• The new dock design (the "shelf")
• The new finder sidebar (reminds me of Windows)