We recently had a short and modest line-voltage sag at home, no big deal. While the incandescent lights dimmed slightly and came back up, nearly everything else was, as logic designers so elegantly say, “indeterminate.” The PC chattered internally and went wild; some of the compact fluorescents lamps (CFL) came back on, but some did not; the displays on the oven and microwave became random segments; and the home network crashed but eventually reinitialized itself.
It was the plain 900-MHz cordless phone, a relatively simple device, which really showed the most bipolar behavior. The base station indicator LED said the phone was cradled and charging even though the phone was absent; the phone itself would not connect and provide dial tone. The solution was the usual tactic: unplug and restart. I unplugged the base unit from its wall wart; that cleared both the base station LED and its operating cycle. I still had to open the phone to disconnect/reconnect its battery, to reclaim that dial tone, though.
I know “stuff happens”, but this particular stuff indicates both how dependent we are on decent line power, and how poorly designed many lower-cost products are for even slight dips in the mains. There are plenty of good voltage-monitor ICs available for line AC as well as low-voltage DC, but they cost money and board space. So end-users, your average customers, have to be prepared to go around and manually reset lots of their appliances.
To add to the frustration, many of these devices have soft, not hard, power on/off switch functions (see “When an on/off switch really does that”), so the user has to unplug the AC cord. That's not a big deal, unless you have to start moving some big furniture to get to the outlet. Would a whole-house line conditioner be a better idea?