Dual-core MBP is fine for me but I want an Air form factor in the 12-13" size and a proper "pro" quality screen.
Lion is like Snow Leopard SP3.
Lion brought:
Mission Control
Automatic versioning of files
Session restoration of applications
AirDrop
Filevault full disk encryption
Improvements to Spotlight
Twitter integration
Multitouch Gestures in Safari
Preview gained the ability to capture signatures from the trackpad
The ability for one system to have multiple active sessions (screen sharing could connect to a secondary user on the system and use it without interrupting the primary user at the machine)
Local Time Machine snapshots for when you are away from your backup volume for extended time periods so you still get the versioning benefits of TM
And that's just the most visible positives.
...feels like more than SP3.