Not based on total posts, I think that this thread actually has the highest record for page views within a few days:
http://www.flyertalk.com/forum/milea...ckets-com.html

I think if I recall, there were more than 100,000 pageviews within 2 days, three at the most. It got picked up off Slate (?) and really got some attention.

As for most posts, actually i thought that some in OMNI were more, especially the countdown, etc.

But I do think that the United Upgrade news has really been visible when you look at the same topic in almost all the other frequent flyer forums. Seems everyone is interested in United's move.