You can play all your Windows and Mac games on your SteamOS machine, too. Just turn on your existing computer and run Steam as you always have - then your SteamOS machine can stream those games over your home network straight to your TV!"
Neither the dialog nor the preview solves the problem that an undo button solves.
If a dialog or preview comes up for every message you send, you just develop a new habit for sending mail (press the send button, then press the send button again on the dialog / preview). If anything, it just creates more of a hassle for the user.
The undo button is for that 'Oh crap!' moment, when your auto-pilot lead you astray.
For those interested, NIST (National Institue of Standards and Technoology) announced a competition to find candidates for the SHA-3 algorithm back in November 2007:
"NIST also plans to host a final SHA-3 Candidate Conference in the spring of 2012 to discuss the public feedback on these candidates, and select the SHA-3 winner later in 2012."
[http://csrc.nist.gov/groups/ST/hash/sha-3/Round3/index.html]
The final SHA-3 Candidate Conference was held March 22-23, so they should be picking the winner any day now.
"In-home Streaming
You can play all your Windows and Mac games on your SteamOS machine, too. Just turn on your existing computer and run Steam as you always have - then your SteamOS machine can stream those games over your home network straight to your TV!"
http://store.steampowered.com/livingroom/SteamOS/