Only developers have full access to the iCloud now.
I don't have a .me email account so I can't go into the Mail app. Although my contacts are not backed up with Apple's MobileMe, I can still go into the Contacts app. It looks just like the Contacts app for the iPad. I don't have a Mac so I don't have iCal. Still, you can go into the Calendar app and check it out. This also looks just like the Calendar app for the iPad.
Find My iPhone has been available on the web for a while even without a MobileMe account. This is just put in a better place with all of the other apps. And then there's the iWork app. Even though I do have Pages on the iPad and iPhone, this feature does not work for non-developers. Can't wait until this goes live with iOS 5. I won't have to use Dropbox anymore.
iCloud.com is a bit buggy. Even if you check the box that says "Keep Me Signed In For 2 Weeks" it won't keep you signed in. At least not from my experience.
I also noticed for some reason I kept typing in my password and it wouldn't accept it. I eventually got it to work, though. I also found this cute response if you don't type in your password correctly:
UPDATE: The day after I was able to get in, Apple locked it down for only developers. I didn't think I was going where I'm not supposed to go but I guess the whole shebang was only for developers. Since many websites got screenshots, I never thought to take my own since I didn't think I'd lose access to it. Anyway, iCloud.com isn't really "magic" unless you have iOS 5.