Depends. Usually it points to poor construction, loose braces or heat damage. If it's one of the cheapy Yammys then probably the first applies, and this is the best fix:
http://www.stewmac.com/shop/Tools/Special_tools_for_Bridges/JLD_Bridge_Doctor.html
Price to fix is usually the part plus the labour to install. So whether it's worth it is down to who does the labour...