I got my late 2012 Mini in November.
I have experinenced some blackouts but they were rare, maybe two or three times a day.
I only had one major colored noise burst that requred turning the monitor on and off.
When it became available, I have applied the EFI firmware update.
Now everything is fine.
Even before the update, aside the occasional flicker,
I didn't have any other image quality issues like fuzzy text, washed out colors or burnt out whites.
I tried HDMI to DVI, Thunderbolt to DisplayPort and Thunderbolt to DVI connections on three monitors:
Eizo ColorEdge CG243W,
Dell Ultrasharp U2412M,
and Samsung Syncmaster XL20 (actually Samsung does not have DP, so I only tried HDMI to DVI and Thunderbolt to DVI).
All combinations work prefectly for me!
Image quality is perfect and the output looks IDENTICAL on both TB and HDMI ports,
connected to DP and DVI inputs on my monitors.
Colors are good, text is sharp and I can see subtle shades of dark and light grayscale patches.
I have added 16GB of RAM and I have just finished a huge Photoshop compositing and retouching job and I enjoyed doing it.
After reading all this horror stories, I guess I'm really lucky!