I use mYTube which is a nice app but when using a slow internet connection (when the download rate can not keep up with the playback rate), the playback stops and codes the full screen session rather than freezes at that moment. I have to restart playback and it starts playing again from the beginning.
Moreover when the playback is in full screen mode how do you pause / stop it ?
Anyone else with this problem ?

Of course, the browser's YT player (on the site itself) works without problems.

you are right. a quick workarounf for this annoyance (till next release ) will be to press the DOWNload button and after the download reaches a "healthy" percent you can then press PLAY. mplayer should start playing the movie while youtube-dl finishes its job
try pressing fullscreen/space(if you have n810)/whatever mplayer has binded as a play/pause button

Just a tip for iancumihai.
You can avoid having mplayer drop off the end of file by downloading it to a file and serving it on a local HTTP server. The YouTube plugin in MediaBox SVN version does it like this. mplayer will then wait for new data after having reached the end of file before it was downloaded completely.