Days ago I get the iOS4 (iPhone/iPod touch OS) on my iPod touch 3rd Generation. My first attempt to test the new OS was how to use the folder feature so I was watching the WWDC10 Keynote.
Folders is very helpful if you got like me hundreds and hundreds apps, you only need drag and drop one app into another, if both apps has the same category then iOS will create a folder with such category, indeed you can change the folder’s name if you want to.
Multitasking, I got fews apps that supports it like Meebo and pdfreader, maybe on the next weeks developers will release their apps with multitask support. I must to confess I love multitasking when I’m into a game while chatting, or reading a PDF, so useful.
Custom background, don’t like, I prefer black background, maybe if I become to design my custom background.
Bluetooth support for keyboards, 
I don’t have an Apple Keyboard yet…. but I don’t edit letters or docs on iPhone.
Multibox integration for Mail, I only got hotmail and gmail accounts, but I redirect all my hotmail emails to Gmail, don’t need it yet.
If there is another feature that I don’t mention it if because I got few time to re-discover my iPod. Meanwhile I’m pretty happy with such improvements.
