From yumsugar's account it sounds like there was a great atmosphere in the place, and I'm sure there was no shortage of volunteers to help empty the glass when the world record had been secured. Check out yumsugar's site for lots of photos from the big event.
The General Manager of the Buena Vista, Michael Carden, was kind enough to answer my question about the exact variety of whiskey used at the café:
Actually, it is the standard Tullamore Dew with a special label stating it is the official whiskey of the Buena Vista.
In the early years of the Irish Coffee Tullamore Dew was the choice of the day. Then Irish Distillers produced a special blend and label for the Buena Vista which we served for years. In 2003 (I think) we moved to Cooley Distilleries for a Buena Vista blend. And last year returned to Tullamore Dew.