As it happens, I received my replacement membership card with an expiry date of August 2011 today (my existing card is due to expire in August 2010). The cover letter says:

"Dear Mr TheDell

As a Cathay Pacific Credit Card member with American Express, we are delighted to present your new American Express-branded Priority Pass membership card, entitling you to peace and quiet at over 600 airport VIP lounges at over 325 airports worldwide. Your new membership card contains a new expiration date, so please replace your current Priority Pass card with this one.

Your Priority Card membership has been provided to you as a benefit of your Cathay Pacific Credit Card. Your membership is provided to you at the Prestige level, which is designed for the frequent traveller, and valued at US$399 per annum. The membership provides free access to all the participating lounges in the program as often as required during your membership period. Accompanying guests may visit for a nominal fee of US$27 per person, per visit, which will be charged automatically to your Cathay Pacific Credit Card.

...

P.S. If you do not use this Priority Pass card, to obtain a replacement upon expiry please contact American Express customer services."