Will update once I get back home from Singapore. This will be the a perfect example on why official unlocked iPhones are the only way to go.

what is the biggest improvement?

Apple does not always specify the changes it makes in minor software updates. As such, the company leaves users guessing and trying to decipher those changes on their own. Some user-discovered changes in iPhone/iPod 2.0.1 include:

-You can now drag an app icon across multiple pages in one motion, rather than having to drag it, drop it, pick it up again and drag it over to next page, and repeat.
-Contacts are now more responsive.
-After installing 2.0.1, each successive backup is much faster.
-Apple may have changed the calibration of the iPhone's reception "bars" while connected to a 3G network to reflect a stronger signal than before.
-Keypad loads quicker.
-Screen rotation in Safari appears to be smoother.
-Some apps may ask to be updated after the firmware upgrade.

Source : AppleInsider