It's all in the title. Do you remember any "decision only main cards" you considered as great events?
I remember a big decision @ ufc 151. I can't remember a card with only decisions right off the top of my head.
The decision not to fight? That was the all time most epic bad decision ever. Screwed over other fighters and fans alike.
UFC 76 called 'knockout' had no knockouts at all, had a sub in the main card but Still makes me laugh http://en.wikipedia.org/wiki/UFC_76
The "preview" article from Sherdog's main page predicted only decisions for the main card. Someone criticized the author in the comment section for it.