I was leafing through a Spanish tapas recipe book written by that Tapas Revolution guy (Omar Allibhoy) who was on the TV. Some very nice recipes in it by the way.
Anyway, in the book he claims that Sherry doesn't go off after it's opened, with the exception of Fino.
I usually keep sherry in the fridge after opening, and to be honest the bottle rarely makes it beyond the week anyway! Mind you it would be nice to have a few on the go knowing that one could keep them for months on end rather than slurping them up quickly. And free up fridge space.
How long do you keep yours?