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The higher priced Samsungs have dual core and quad core is coming (and available to some models as a plug in upgrade).
Got a dual core in mine and it's reasonable speed for what it is. Remote entry for text is still a pain, but that's not what Smart TV is for. It's select and click (or gestures on the fancy ones).
Quite happy with mine, and I'm surprised I'm getting regular updates. That the app updates only occur when you launch them is a little niggle but happy they have them (apart from Red Bull TV which still doesn't have a fix to the annoying audio stutter on their live TV feed). Also happy that there are newer apps coming along.
UI on the latest is relatively clean if annoyingly populated with "social" guff in parts.
The really rubbish bit however is the DLNA interface. It finds the servers okay but then it's a clunky interface of folders and cryptic names. Then again it's arguably the DLNA server at fault. Hence the likes of Plex to make them more informative, but then they've also gone and made an app for Smart TV anyway (not available on all Samsung models yet).