If you have 50 Amex cards (5 Amex cards with 10 AU's each), you'll still get $500. How long will it take you to register all these cards? An hour? 2 hours? If that's not worth your time, then I'm sure the $25 per card wasn't a big deal either for most people on this forum. C'mon ppl, it's free money, if you don't like it, don't register - but don't complain either.
If you don't have 50 cards, then now's a good time to start adding some more!