One man's trash is another man's heirloom, and vice versa. Before you go giving away your beloved, gilded-poodle china set, ask yourself: Is this something my son/daughter/cousin/niece would want?
Granted, it's hard to know, but there are a few criteria you may want to consider. First, has it actually been passed down through family generations? Next, is this something that anyone besides you may actually use, display, or love, or is it only for someone with very specific (and rare) taste? Finally, has anyone in your family expressed interest in it? Admired it? Claimed it?
Were you happy to have inherited it?
If the answer to most of these questions is yes, than you've probably got yourself a family heirloom that's worth designating.
That's the easy part. The next decision is one that could haunt your family for generations (no pressure).