I have done some more digging and there are big changes to the referral bonuses and the rules to get them.

The full details are here
http://headforpoints.com/2012/07/05/...-new-criteria/

but basically:

Amex Plat - sign-up now 50,000 points with £100 Quidco. However, you must be a new Amex customer to qualify, that includes not having a BA Amex. Income target raised to £40k from £30k.

Amex Gold - fee waiver in Year 1 now not available if you have an Amex charge card already. 20,000 MR points only given to new Amex customers which excludes BA Amex holders. Quidco doubled to £20.

Overall - not good for card churners (and aren't we all!). Now it will be more about referring our partners for cards, although a lot of us already have a BA Amex for our partner as well.