Can I use the new @me.com address as a full feature mailbox? When setting up iCloud in my iOS 5 iPhone 4, there is a new @me.com address created (Settings > iCloud > Account > Advanced > Mail 

Is this new @me.com a full feature mailbox?
Yes - iCloud includes full mail service - webmail, IMAP and iOS for free and not counting against your free 5 Gb of cloud storage quota.

http://www.apple.com/icloud/ mentions that iCloud is free with iOS 5. Enjoy!