With iOS 4, you'll be able to multitask (for non-magical sparkling pony values of multitasking), use folders to organize your apps, jump into the unified e-mail inbox, and more.
So how's the download going for you? And did it install without problems? We're particularly dying to know if the 3G installation performs better on the real Gold Master firmware release than it did during the beta period (it ran like a dyspeptic dog). Let us know in the comments how your iOS 4 upgrade went -- and how you love (or hate) the new feature set.
For those of you who are curious, yes, this is the same 8A293 build seeded to developers with the GM release candidate. We're guessing that Apple needed to put that onto the iPhone 4 devices you'll be picking up later this week and stayed at that build for the final public release.
Don't forget, you will need iTunes 9.2 for your new iOS 4 installation. Also, iPhone 3G users may need to do a full restore, not just an update. So your update may need to take a bit of extra time as you re-sync your data from your most recent backup.
Update: Live in iTunes now!