Forgive me for my ignorance.  Let me see if I understand this correctly:

If I am a "first time homebuyer" and am considering buying a house in 2009 then I can go ahead and deduct the $8000 from my 2008 estimated taxes????  I then file an extension and pay the estimated taxes.  If I buy a +$80,000 house during the year, then all is good.  But if I don't buy a house, then I need to "correct" this mistake when I file 6 months later.  Is there any penalty in the latter senario??  Or did I misunderstand?

Also, I am still a little confused as to the definition of "first time homebuyer".  Here is what the IRS says:

A "first-time homebuyer" is any individual (and spouse if married) who had no present ownership interest in a qualifying principal residence during the 3-year period ending on the date of purchase of the principal residence for which a first-time homebuyer credit is being claimed.

I currently rent the place where I reside (I do not have any ownership interest in my current "principal residence").  I do own several houses, but do not reside in any of them (rental properties).  So, if I buy another house in 2009 and make it my "principal residence", then I qualify for the the credit.  Correct?