I agree that real estate is definitely local and that you should speak with a LOCAL Realtor in your area so they can help you determine where your price should be. Remember, a Realtor cannot give you the "appraised value" for your home, instead they can put together a Competitive Market Analysis report and give you a general idea as to the "fair market value" of your home. There is a BIG difference between the "appraised value" and the "fair market value." An appraised value is only a value and in no way guarantees that value is what you will be able to sell your home for. A fair market value or estimate on the other hand should tell you what you would be able to actually list and sell your home for. In the current "BUYERS MARKET" that we are experiencing, this can sometimes be very difficult.
As for the % of loss incurred year over year, that is a very generalized number and there is no set number that we can really go by. All I can say is that in my areas that I serve (generally Northeastern Baltimore County and all of Harford County), the market prices have definitely come down around the 10% range within the past year. However, they appear to be stabalizing recently and even starting to increase a bit (in certain price ranges). The price range that is getting the most activity in my areas right now is the $250,000 and under range. Generally speaking, in the Baltimore County & Harford County areas, this would basically buy you a middle of the road townhome, nice condo, or an older single family home that needs some updates.
You can certainly research your specific areas statistical data from http://www.mris.com
and click on the market statistics page and then enter your zip code, county, etc..
Hope this helps a little.