Derrick Stolee [off-list ref] writes:

Singular "they" works the same as singular "you". For example:

	...means that _you are_ completely satisfied...

Singular "you" had a similar backlash in the 1660s as singular "they"
is having in this thread, but singular "you" has lasted (and we use
"thou" only to signify someone using old-timey language).

Oh weird... the big debate with you always was that we have no plural
version of it to use when referring to a group of people, and it was
plural all along, but is still used when referring to only one person.