Well in Preview, the functionality was moved to the new "Sharing" functionality. Click the arrow in the toolbar and choose Email and it will be emailed as an attachment. This arrow is also available in the open dialog.
As far as smart mailboxes, I think creating a smart mailbox for a recipient is probably just replaced by the new VIP functionality. It performs the same role as the smart mailboxes you were creating.
You can create smart mailboxes for other things, and that functionality is the same as it's always been.
The Preview App in Mountain no longer has email as attachment. What happened?
To send as and email, click the share button in the tool bar.
It's the little square with an arrow pointing out of it.
Also, creating smart mailboxes in Mail is so much different. Before I used to Option click on recepient address to make a smart mailbox. What happened there?
I've found the fastest way to create a Smart Mailbox for a recipient is to type their name in the search field and then click the Save button.