Basically, there's no "regular" tax liability, but the difference between the exercise price and the market price at time of exercise counts as income for AMT, and so have a great day, you're gonna pay AMT that year if you do this for any significant quantity of stock.
You missed my point. By pre-exercising my ISOs and filing an 83(b) with the IRS showing that the exercise price and the market price were in fact the same when I exercised, the gain was zero, even for the purposes of AMT. Not everyone will be so lucky to be in that situation where the prices match, but I was.
Here's a site on it: http://fairmark.com/execcomp/isoexer.htm
Basically, there's no "regular" tax liability, but the difference between the exercise price and the market price at time of exercise counts as income for AMT, and so have a great day, you're gonna pay AMT that year if you do this for any significant quantity of stock.