In short, deficiency judgments. Even if your first mortgage were to agree to foreclose without a deficiency, you would still be facing the 2nd and association fees.
You should contact an experienced bankruptcy attorney, well versed in foreclosure law, and explore your options.
This question is so common. Attorney Larson is absolutely correct. These matters should be resolved as early as possible. So often they are not.
I hope this helps.
Steven A. Leahy
Please note that the above is not intended as legal advice, it is for educational purposes only. No attorney-client relationship is created or is intended to be created hereby. You should contact a local attorney to discuss and to obtain legal advice.
There are options you can pursue on your mortgage: HAMP and HAFA. However, these programs will not help you with the association dues that you owe. You should engage an attorney experienced in foreclosure defense and bankruptcy to help you with your situation.
Disclaimer: This answer is provided for informational purposes only, does not constitute legal advice, and does not create an attorney-client relationship. Actual legal advice can only be provided after completing a comprehensive consultation in which all of the relevant facts are discussed and reviewed.
For purposes of the facts as you have outlined them, I am assuming that this property is your primary residence and that you have no other significant debt issues other than your underwater mortgage. With these qualifications, it seems to me that your best bet would be to attempt a short sale on the property. However, generally speaking, you cannot be current on your mortgage for the lender to consider your short sale request.
You ask what you should be worried about other than the effect on your credit. You should be worried about the Association obtaining a personal judgment against you for the amount you owe in past due assessments. In a short sale, you can negotiate with your lender to satisfy the Association debt as part of the sale - however, the Association may require you to contribute funds to completely settle the debt.
If you have not already consulted with a realtor and a real estate attorney, you should do so immediately. While it does not sound like it is too late to salvage your situation, the worst thing that you can do with an underwater mortgage is NOTHING. There are many, many solutions for underwater homeowners - doing nothing is not a solution, it is ignoring a solveable problem that will only get worse if you do not take measures to help yourself NOW!