Today is the day that all the wonderful things we heard about during the WWDC keynote regarding the future of the iPhone OS, now officially dubbed iOS 4, are available to everyone. This update is completely free, and only requires you to plug your device in to the computer you usually sync with then waiting for it to download and install in iTunes. There are over 100 new features in iOS 4 according to Apple, but so far my favorite two are folders and multitasking.
With folders, you can now have up to 2160 apps on your device, and multitasking now allows for apps like Pandora Radio [Free] to continue playing in the background. For a listing of the other features, take a peek at the Apple iOS 4 Software Update page.
One unfortunate thing to come out of this update is that first generation iPhone and iPod touch users are being left in the dust. If you have an older device, you will be stuck in 3.0 land, and only the third generation iPod touch, iPhone 3GS, and iPhone 4 are capable of multitasking.
Before updating your device make sure you not only do one full sync to back it up, but you also check and make sure there aren't any issues reported with your favorite games running on iOS4. For instance, ngmoco just tweeted warning players of Eliminate [Free] and Touch Pets Dogs [Free] of potential performance issues while playing the game on iOS 4.
I've yet to encounter any serious issues in the games I regularly play, and many games and apps have had recent updates that have added iOS 4 compatibility. This is just something you should potentially be aware of before mashing that check for updates button in iTunes.