Looks like my cable modem has served it's last bits, or my signal suddenly got weaker for no good reason. I'm reduced back to *gasp* dialup, while I await the princely arrival of Comcast's technician - which won't be until Thursday. Oh, the joys of great customer service from the local monopoly...
Update: I should know better than to take the word of Comcast phone techs. He said that "there was no problem in my neighborhood" - which certainly explained the truck parked by the cable box up the street, with two technicians replacing a circuit board. The good news is, I don't need to wait for the service tech now.