The median price for homes sold in Gloucester, MA in 2005 was $367,000 while so far in 2007 the median price has been $337,250.
Now this includes all types of properties - condos, single families and multifamilies. So it really means nothing if you are using this info to figure out what a specific property is worth in todays market. To be more accurate, you need to break it down into type of property, sq footage of living area, lot size, number of bedrooms and year built - minimum. You have to compare apples to apples if you are using this method to determine property values. Of course, this is not an extremely accurate way of determining value unless it is a condo complex and all properties are exactly alike.
The thing about real estate is that all properties have individual characteristics that determine value. The rest of the market could be going down, but if you are in a very desirable area, your home could hold it's value much better than other areas even in the same town. This also applies to the house itself - what was "in" and desirable by homebuyers in 2005 may not be wanted by the buyers today (think Pergo/laminate floorings).
The only true way to accurately find out what your home is worth is to contact an experienced Realtor or appraiser. I personally believe a Realtor has a better handle on market values because they talk with buyers everyday about what they are looking for in a home - and it not just because I'm a Realtor.
I hope this helps. Contact me if you have any other questions.