Is it possible to stream a tablet screen to desktop via bluetooth to a PC? This way you could give a presentation (and make annotations), show movies on your tablet and stream it to your PC/laptop which is connected with bluetooth (in e.g. a classroom) with no need to go to the PC.

Has anybody used this setup?

As a teacher it would make a smartboard out of my tablet (which i would buy for this purpose, amongst few others) and a simple bluetooth dongle which I could plug in the school PC.

Looks simple to me, but probably isn't as simple as I imagine? 

I'm even prepared to pay a fee for an app if this is available.
I do not know of a way to display your tablet screen other than some sort of display adapter. Things like this with the receiver would allow you to do it wirelessly, but they get mighty expensive.

Additionally, I do not believe bluetooth is designed as a "Display out" port, so to say, and I am hard pressed to believe it would be easy to do this, beside the fact that you may need to write that yourself.

I would recommend something like Splashtop Remote. This does not display your tablet screen on the PC  but allows you to see and control your PC screen from your tablet. So you could not share your tablet screen, but you could still walk around the classroom with your tablet and control what is being projected to the screen.

Also, and I don't know if this works over bluetooth, but you could try the Android Screencast Project. Maybe it has what you need!

I know it's not the solution you're looking for, but hopefully it helps!