Beppi Crosariol has a good article in the Globe and Mail arguing against ordering wine by the glass. I know what he means: once, I ordered a glass of red from a good restaurant and it was warm because the bottle was sitting on the bar fridge! Ugh! That went back.
If you want to order by the glass, see and order what was recently opened, and try and stick with fresh whites. (What is true for glasses also goes for 1/2 litres and anything that comes from an opened bottle. Although in some cases, if it’s a recently opened red, you may get the benefit of the wine opening up a bit.)
See for yourself by reading this: Wine by the glass? I’ll pass
P.S. He also had a nice, snarky comment (on this varietal) that I love:
“(Hey, if you’d wanted a white wine with no flavour, you’d have ordered a pinot grigio.)”
There are some pinot grigios that do have flavour, but why chase them around when there are so many other white varietals that do have taste?
(flickr photo from sunnyUK photostream)