I don't think the Value matters as much as the 2 capacitors being the same.

Another quote from the datasheet...

Higher capacitance increases the stability
of the oscillator, but also increases the
start-up time.

If you have different value caps then it will change the frequency.

I've been using some 12pf caps that came with the 32768 crystals I bought. And it keeps real good time.

DT