Great information. The best place to find all the facts is actually the IRS form. See www(dot)irs(dot)gov/pub/irs-pdf/f5405.pdf (replace the (dot)s with “.” .

So if you do sell the house within the 36 month period, your repayment amount is LIMITED to the GAIN on the SALE PRICE. (see below)

Here is the meat of it, FYI:

Homes purchased in 2009. You must repay the credit
only if the home ceases to be your main home within the
36-month period beginning on the purchase date. This
includes situations where you sell the home, you convert
it to business or rental property, or the home is
destroyed, condemned, or disposed of under threat of
condemnation. You repay the credit by including it as
additional tax on the return for the year the home ceases
to be your main home. If the home continues to be your
main home for at least 36 months beginning on the
purchase date, you do not have to repay any of the
credit.
If you and your spouse claim the credit on a joint
return, each spouse is treated as having been allowed
half of the credit for purposes of repaying the credit.
Exceptions. The following are exceptions to the
repayment rule.
c If you sell the home to someone who is not related to
you, the repayment in the year of sale is limited to the
amount of gain on the sale. (See item 8 under Who
Cannot Claim the Credit for the definition of a related
person.) When figuring the gain, reduce the adjusted
basis of the home by the amount of the credit.
c If the home is destroyed, condemned, or disposed of
under threat of condemnation, and you acquire a new
main home within 2 years of the event, you do not have
to repay the credit.
c If, as part of a divorce settlement, the home is
transferred to a spouse or former spouse, the spouse
who receives the home is responsible for repaying the
credit.
c If you die, repayment of the credit is not required. If you
filed a joint return and then you die, your surviving spouse
would be required to repay his or her half of the credit.