Great thread!
Couple things I found (99% sure they're new in 3.0):
1. If you had a WebApp bookmark on one of your homescreens, and had set it up in 2.x when that particular website didn't have a favicon, when you click on that WebApp in 3.0 and a favicon now exists for that website, the homescreen icon will auto update to the new favicon...before, you had to re-add the webapp to your homescreen.
2. This might have been mentioned before, but in "vertical" stocks, when a particular stock is selected, if you "swipe" the mini-graph left, then a more detailed stock quote will show up with Open/High/Low/Volume/PE/Mkt Cap/52w High/52w Low/Avg Volume/Yield...and if you swipe another time to the left then news for that stock comes up and the news is scrollable in the vertical direction.
3. if you click the arrow on a recent calls contact person, it will show you the duration of the last few phone calls in minutes. It's also easier to add a contact to your Favorites now.
4. You can redeem gift certificates and "beta app redemption codes" from the App store.