At the risk of incurring Hookbill's wrath for another post on 2.3... I am interested in what members here think the greatest feature that 2.3 could add would be. If you have any candidates that you feel I have omitted let me know and I will likely add them.
To explain each option a bit,
1. A GPU accelerated GUI is what makes the user interface of the iPhone and WP7 so much smoother than Android.
2. NFC would allow phone users to use their phone as a credit card
3. FM Transmitter would allow users to stream their music to any FM radio
4. This one is open to interpretation, not a gamer myself but I frequently see this request
5. The Email app doesn't support IMAP and lacks many other gmail features
6. Tablet-atization, would involve requiring all apps to support tablet screen resolutions and tweaks to the Google Apps and UI
7. WAAS makes GPS 20x more accurate (according to specs) and enables faster fixes, most new dedicated GPS handheld units now support WAAS.