I had previously thought (as has some commentators) that the tax liability can have a discontinuity jump if the Line 38 1040 amount goes over a lower amount. This does not seem true, as if you follow through Part II of the 6251 and then lines 44-45 of the 1040, you can find the "interpolation". Still, the tax is steep and for 2012 would not be in line with other tax rates. Most seniors would not have an issue if Congress keeps the amount at $48450 or increases it during the lame duck session. There seems to a lot of confusion (even among tax preparers) as to what really will happen if Congress fails to fix the 2012 amounts.
The AMT rules could provide very perverse incentives for some seniors not to work part-time when they otherwise would, because they could be penalized big time for having adjusted gross that reaches the exemption threshhold. Congress must fix this problem. It is a gross, self-inflicted public policy blunder with major economic consequences.