Here's a piece of new functionality with iOS 5 Weather app.
The Weather app doesnt look like it has changed much, but when looking at the forecast for the week, tap and pull down below a day and it will give an hourly forecast.
[crarko adds: Hey, that's pretty cool. I hadn't noticed this before.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20111216162509206