We've certainly been doing our bit to seek out new merchants taking AMEX and pressure those that don't (either directly or just by walking out when they say "no AMEX" - making sure they know why).
Two thoughts that would certainly help me to use my AMEX a lot more - not just for the promo but on an ongoing basis:
1. No signature required for very low value transactions (say under $10). Actually had my local butcher do this the other day unexpectedly for a $5 transaction. I was waiting to sign and he said "No worries, you don't need to sign for that amount". That would make it more convenient as a cash replacement, saving some time for us and for the checkout staff.
2. If AMEX could do something to discourage minimum spend on cards I'd certainly appreciate it. Obviously it would be nice during the promo, but on an ongoing basis there are at least 3 restaurants within spitting distance of work that I would eat at one of every day if they would allow their lunch specials (about $6) to be put on AMEX. As it is with $10 or $15 minimums I have almost never been for lunch.
The whole minimum spend thing always seems like a bit of a wank really, given that the merchant fees are just pro rata and there seems to be no real reason for not taking say $5 on a card. Sure it's maybe 30 seconds of staff time to handle the swiping, but not really so much different to say issuing change from a $20 note or some such. (And, in combination with the first point, if no signature was needed on a very low value transaction it would save everyone some time too).