How good are scallops after being frozen?

That all depends on the method of freezing and the means by which the scallops are kept frozen. Vacuum sealing and flash freezing is the best method for the actual freezing process as this causes the least damage to the meat. Keeping the meat frozen at -20 F (-29 C) will allow the meat to keep almost indefinately. Most of us do not have access however to the proper facilities and appliances for this so here is an easy way to tell if the meat is no longer edible. Look for dry, flaky white areas on the meat (also known as freezer burn). If there are areas like this on the meat, then it is no longer edible. If you have store bought, vacuum sealed meat, then look for ice crystals developing under the plastic. This will indicate that the meat is no longer edible.