Though I love AS dearly, here are a few things that have made Mileage Plan worse recently:
1) The loss of NW F upgrades
2) The loss of CO for earning RDMs and redeeming awards
3) The doubling of the B of A companion coupon price.
4) The imposition of BA's fuel surcharge on award tickets (which is also imposed on BAs own FFs, but not on folks who redeem via AAdvantage).
I know the grass isn't necessarily greener, and I know that none of the stuff above is even AS's fault, but it still affects the value of the program and adds to the perception that it's not quite as good as it used to be. I'm not going anywhere (in the short term at least), but wouldn't be surprised to find out that others might start checking out UA or other options.