Is there any way to type into the opera search box or address bar and have the result open in a new tab by default (i.e. when I simply hit enter)? (Opera 10.52 beta)
Yes. Just press Shift+Enter instead of Enter and you'll get what you want.
This key combination works for any search box or address bar since earliest Opera releases.
EDIT: Also if you copy the address or search words to clipboard you can press Ctrl+Shift+V instead of standard Ctrl+V and Shift+Enter key combinations. This will paste text and open the result in new tab immediately. Try it.