iPhone 3GS and 3G owners, plus iPod Touch-users, time to plug in to your computer and download iOS4. It's here.
We're getting reports of the iOS4 being live, and it's currently being downloaded by users right now. If it isn't live for you yet, keep hammering that update button until it is. (Because if you can't get it, then you might as well slow things down for people who can. I kid, I kid.)
You'll need to have downloaded iTunes 9.2 (and you should run a manual back-up if you haven't already). It's the only way to get the brand new features in Apple's latest OS that they announced a few months ago, including multitasking, fast app-switching, local notifications, and iBooks. For the list of the best new features, mosey on over here, otherwise check out the official line from Apple below.