Singular They works perfectly fine, and anybody who says otherwise is a fool. :I
For those worried about correct "traditional" usage, Singular They goes back to at least the time of Chaucer and is attested in much of the "great" literature. Forcing it to be plural only goes back to the late 19th century and is an artificial construct by linguistics experts, not actual language speakers or respected authors.
In fact, Singular You is even more bullshit than Singular They if you go by the same arguments made. One main argument against Singular They is that "they is" sounds wrong hence it can't be singular. Apply that to "you is" and you see the flaw with this argument. An objective argument must hold as a general case, and this doesn't as long as you accept "you are" as a singular usage as well. In fact, Singular You is a recent construct. It used to be plural only, with "thou" being the singular version. Thou disappeared and You became ambiguously singular or plural. So the argument that the plurality of "they" is ambiguous and therefore it shouldn't be used also applies to the word "you", and we don't see anyone calling for a return to "thou".
So, Singular They wins out in terms of historical basis and usage by the greatest writers in the English language, and the only syntactical arguments against it fall flat on their face when compared to other word usages like "you". Also, our usage of You as singular would be reviled by the classic novelists as abhorrent misuse of language.