I missed the AMT. From the looks of things, it goes like this for most people:

Take your taxable income 1040 line 43, add back the exemptions you took on the front of the form (self, spouse, kids), then add back the total of taxes deducted on schedule A in the "taxes you paid" section. If that figure is over about $44000 for a single or $66000 for a couple filing jointly, you're at risk.

I'm surprised how close I was. I earn less than $55k per year, and write off less than $3000 in total (income + property) taxes. If it wasn't for the changes that SilentAltima described, I would have probably been another unhappy AMT customer. Of course a larger income is a factor. But also it appears that those taking large exemptions (i.e. children) and/or residing in states with higher taxes (property and/or income) are at a disadvantage.