I have my macbook 2.0 hooked up to my sony Bravia 52 LCD TV and have no issues playing 720p mkv's with Plex. However when playing 1080p mkv's the audio often goes out of sync with the video. The macbook has no issues playing these files on a normal pc lcd. I have not figured out how to remedy the audio sync issues yet.
I am thinking about switching over to a dedicated media player for my tv such as the new Popcorn Hour C-200. This media tank plays everything that you through at it.
www.popcornhour.com