This thread was inspired by the one about Seasoning the Glasses.
Years ago, when I led my first tour of Burgundy, we spent a day with the folks at the Burgundy Wine School. We started out with a basic tasting class. The leader started us off by saying everyone should pick up their empty glass and sniff.
I thought I knew thing or two about wine, but had never heard (nor thought) of this before. He said one could eliminate much of the "off" wine because sniffing the empty glass can easily reveal soap residue and other off aromas. One of my travelers said she smelled nothing, and the leader said that was what she wanted to smell.
So interesting. and it has, over the years, saved many an "accident" especially in restaurants. I try to grab the glass before the waiter (or sommelier) has poured any wine into it and sniff. Lots of waitstaff roll their eyes, but hey! it works. ;)