This just hit my inbox:

Add a card member to your account and you can earn 2,5000 bonus miles after your additional card members spend $500 in eligible purchases on their cards within their first 3 months.

If your additional card member just buys 1 point purchases (which is pretty much everything), you end up with 3,000 points on $500 of spending (2,500 bonus + 500 regular points).

This is a very nice 6x points per $1 on that $500 spend.

Or you can combine with Skymiles dining for even better results.