I completely disagree, my company (Fashiolista) advertises almost exclusively on Facebook. The results are great. My reasoning why Facebook works so well can be found here:
http://www.mellowmorning.com/2011/09/21/5-ways-in-which-face...
There's nothing to disagree about. The guy just pointed out what happened.
Besides, "I completely disagree" is just code for "You're wrong".
I completely disagree with that statement :-D
"I disagree" is a statement of opinion -- I believe something different than you do. "You're wrong" is an assertion of fact -- your belief is incorrect. The former is much less of a direct challenge to the other person than the latter is.