iOS 5 Supports S/MIME Encrypted Email
Here is an interesting iOS 5 feature that Apple doesn't seem to be advertising very much (since most people probably don't care), the ability to use S/MIME to sign and/or encrypt e-mails sent from you iOS device. This is actually a pretty killer feature for me as I like to sign e-mails I send (of course I used a self-signed certificate so it shows up as invalid unless I send my public key to recipients).