: yes! you can finally multitask on the iPhone! Suck it, Android! Actually, the iPhone could already multitask, in a very limited sense, and only with Apple's proprietary apps. Now, third-party apps will be able to run in the background. You can listen to Pandora while you play some Plants Vs. Zombies! Talk on Skype and toot on Twitter. Using some fancy code thingies, apps you love will be able to easily switch back and forth, each one being 'flash frozen' in whatever state you left it in, ready to be brought back into the same state as you left it.
: Now you can organize and store apps within folders. Just drag and drop one app onto another an a folder is created to store them. With folders, an iPhone can now hold over 2,000 apps! Holy fuck that's a lot of fart apps!
New Mail App
: The Mail app is getting a few very nice updated, including threaded conversations, as well as a unified inbox, so you no longer have to jump between several inboxes on different email accounts.
Bluetooth Keyboard Support
: for when you to take a crack at writing the next War and Peace on your phone. Actually this is pretty great if you want to travel really light but still want to be able to have an extended conversation through email or IM or whathaveyou. Should even include copy & paste functionality.
: goddamn APIs! Over a thousand new ones! Holy fuck that's a lot of APIs! APIS!
Camera ZOOOOOOOM: TIMES FIVE. PLUS, VIDEO TAP-TO-FOCUS. Also apps now have unfettered access to camera APIs and metadata.
: Apple's vision of what mobile advertising should be. As Jobs said it during the keynote "Search isn't where it's at on mobile devices." Created using HTML5, iAds can be immersive, interactive, and can help app developers make some money from their free apps.
A whole bunch of other cool shit!
All of this is awesome, right?
If you own a 3GS or the latest-gen iPod Touch, fuck yes it is! You get all the features of iPhone OS 4. If you own a 3G, you get some of these new features, but you're not getting multitasking, sorry don't have enough RAM to handle all this new multitasking hotness. If you own an original iPhone. . .well. . .your contract should be up for renewal soon, right? The next-gen iPhone is likely right around the corner! If you've got an iPad, you'll have to wait till Fall before you get these new features.
Anyway, if you've got about an hour to kill, check out the actual keynote, it'll help you understand how some of these things work better. Also, learn how Steve Jobs would decorate his imaginary dorm.