Apple began its Wordwide Developers conference keynote today by showing off Mac OS X Lion again, and unveiling the new features of iOS 5, while of course sprinkling in various stats about Apple’s accomplishments. Though CEO Steve Jobs introduced the keynote, he left other Applers to demo the OS updates.

He then returned to demo the much-anticipated iCloud, which he is “really excited about”. He also said Apple is demoting the the Mac and the PC to “just be a device,” and “move the digital hub, the center of your digital life, into the cloud.”

“iCloud stores content in the cloud and wirelessly pushes it to all of your devices,” said Jobs. “It automatically uploads it, stores it, and pushes it to all of your devices.”

MobileMe apps have been re-worked to work with iCloud. Contacts can be added in any device and synced to all devices. The same goes with calendar editing.

Users can get an @me.com account to have all messages synced across devices. Jobs emphasizes that these accounts will not have ads, saying, “we just don’t want ads.” A dig at Google perhaps? Gmail shows users ads based on text in their email conversations.

MobileMe now “ceases to exist,” according to Jobs, and iCloud is free. Apps can be accessed from any device, as can books from iBooks, music purchased from iTunes, photos, videos, etc. Specifically, iCloud supports:

– Automatic daily backups to iCloud over Wi-Fi
– Purchased music, apps and books
– Camera roll (photos and videos)
– device settings
– App data.
– Documents in Pages, Numbers, and Keynote

You can simply enter your password on any device and access your stuff (kind of like what Google’s doing with Chrome OS).

It works across all iOS devices, as well as Macs and PCs.

In terms of photos, the last 1,000 will still be stored on the device.

Then of course there’s iTunes, where music can be accessed on any device without multiple purchases, of course. iTunes is getting a new “purchased” tab, which shows you the stuff you’ve bought download it to your device.

If you have music that you’ve ripped yourself (as opposed to downloading from iTunes), you can now use “iTunes Match,” which scans your music and matches it up with songs in the iTunes store in “minutes”. iTunes has 18 million songs by the way. Matched songs are upgraded to 256 kbps AAC DRM-free, and songs that don’t match will be uploaded. One catch – iTunes Match costs $24.99 per year.

iCloud is free, it will be available by default on iOS 5, and it comes with 5GB of storage for mail, documents, and backup. Purchased music, apps, and books don’t count toward that, nor do photos. iCloud is launching in developer beta today.