I've found some AMT credits that TurboTax wasn't giving me, because it didn't fill in values from 2008 and 2009, even though I've been using TurboTax every year since at least 2008.
When filling out your 2011 Taxes, be sure to follow the interview questions for Credit for AMT Paid in Prior Year. You can see it in the Deductions and Credits page as such:
Next check the values on this screen:
TurboTax seems to have carried over the correct values for me from 2010 (I blanked them out in the screenshots, sorry).
And check the 2010 Form 6251 Amounts, which for me also seem to be correct:
The following screen is, I believe, the reason why I wasn't getting a credit:
These values were blank. Once I looked up all the values from my previous returns, and filled them out correctly, TurboTax computed an AMT credit for me.
There's some discussion of this on the Intuit Community site.
And as always, consult your tax advisor.