I do like the idea of SmartGlass, but some of the features are useless.
The first one is a gimmick and I assume only selected games will use it. It'll be cool at first but after a week or so it'll never be used again.
Browsing on consoles is crap anyway. If I'm browsing the web on my phone/other portable device, it's only to quickly check something and I wouldn't want to send the webpage to my TV. I assume your Xbox has to be on the dashboard for this to work? So you can't for example, be playing a game on your 360, check a walkthrough on the web via your tablet/phone and then send it to your TV, can you? If you can then that's pretty nifty. TBH the only time I use my phone to browse the web is when I'm either playing a game or when watching TV. With the latter I won't even have my console on.
The watching movies bit is again, pointless. Who watches a movie on their tablet if the TV is in the same room and the Xbox is on, not being used? Same with music. I don't know anyone that uses their TV for music. Most people have a dock that they just plug their device into.
Real time cast information is again a gimmick which you'll use once or twice. All it does is distract you from the film.
I don't understand what you mean by gestures. The keyboard/remote control bit sounds good but isn't that what the controller is for?
So yeah, I like the idea of SmartGlass. I like it when multiple device I own interact with each other, but most of the time it's just a gimmick. It's like Remote Play on the PS3, it has potential and I like the idea but most of the time it's utterly pointless.

