I propose a new model -- customers should be paid for upgrading to Mountain Lion.
My experience is that every new cat breaks enough software and causes enough disruption that this cost is far more than Apple charges for the upgrade. Going to annual upgrades, even at free, will cost me far more than the biannual $29 upgrades did. It's the same problem that Firefox has gotten into (how many people like its new short upgrade cycle that breaks all the plugins every time?) or the frequent upgrades of Linux distros.
Can't we have an upgrade that fixes bugs (there are plenty of Lion bugs still around), maybe adds features, but doesn't remove features or break existing applications?
Or would that just be a "service pack"?