I have watched some movies using version 0.4.1. MKV playback is smooth however there are two situations which show some problems:
Pausing / fwd/rwd the movie, after one of such operations the movie starts stuttering, playback resumes fine for a few secs and then starts to stutter, from which it doesn't ever seem to recover. In fact the audio is stuttering, the video looks somewhat slightly accelerated. If you pause playback while stuttering and press play again, it plays fine for a few secs, starts stuttering, and so on.
The same actually also occurs without pausing the movie, however it happens at a random point in the movie. Stopping the movie and playing the movie again gives me an error that the movie is corrupt on my player.