Question: If I'm making Homemade Jams/Preserves, how long will they last?

Answer: 
All home-canned food should be used within a year. This assumes you follow the strict sterilization regimen required by jarring/canning at home. You should also store them in a cool, dark, dry place between 50-70°F. 

Over time changes in color, flavor, and texture is inevitable. This will result in a degradation of *quality* in the product, but as long as the seal is in tact and there are no visible signs of mold or yeast the jam should be safe to eat.

Another thing to note is that lighter colored jams tend to darken faster than others and thus may not look appealing over the course of a full year. They are still "safe" though.

Source:

<http://www.uga.edu/nchfp/questions/FAQ_jellied.html#7>
There's also freezer jams, which can easily last a few years in a deep-freeze without losing much quality. They're well sealed, so there's little moisture loss / freezer burn, there's little loss of quality aside from the initial freezing, and you don't have to worry about mold or other organism growing in the freezer.