I think this is something wrong: as far as I know, if you are experiencing a flickering problem every few seconds, it will keep flicker also over 30 minutes.
We are all waiting the official Mac OSX Montain Lion 10.8.3 release since it should fix all these flickering issue (I've read somewhere people trying latest beta confirm this).
What I'm wondering is why Apple, that know this issue very well, wants to wait this release and don't post a OSX fix before the 10.8.3 release. It seems there are a lot of people with unusable minis. That is something sound curious.
I use the mini connected to my HT to watch videos, iTunes films, Youtube, Plex etc., so nothing really urgent and I'm temporary place my mini in its package waiting for the fix. I'm using an Apple TV instead with all its limitations but happy in the meantime. For who owns Sybology NAS products, if I'm not wrong, I've read there is a 4.2 DSM beta that allow to stream Plex directly into Apple TV in AirPlay. This sound fantastic, waiting for the official release to test it. Happy new year.