I have gotten it to work. Basically, just type in a random screen name, and your address.
Once that is done, click on start screen. Then launch the app, and it will use GPS to match the address you just entered. (Sometimes this does not work, so you can search for your PC through your screen name manuallly as well). AS soon as you find your PC, start searching and playing YT videos with the inbuilt search in the app. And voila, it will start playing on your PC.
As a side note, i also tried doing this through my PS3 browser on my TV, but it did not work. I think it needs Flash or some other plug in, that only a PC seems to have right now...