A search for the product's name or handle on Twitter to detect a surge of activity post-deploy.

(Most surges are negative, eg. "Man, <YourService> is down AGAIN, this sucks.")

I assume watch a feed on Twitter for a search about your company or product. If people on Twitter start complaining in mass about your latest push it's probably a good sign that you need to roll back.

Ok, this is what I also assumed - although I would never rely upon this as part of my continuous deployment process, I guess it does little harm to still monitor and be aware of such things...

At Flickr, I always have our system graphs in one tab and our help forum in another tab.