If you have Comcast and are wondering why your cable modem is coughing, sputtering, and pages are loading s l o w l y, apparently Comcast experienced a system-wide DNS server failure today.
DSL Reports.com (which also has a newer URL called Broadbandreports.com; both access the same site.) has a possible solution. No guarantees of course, that it will work if you’re experiencing similar problems, but it worked for me. Pages are now loading relatively quickly, although perhaps not as fast as before the problem developed around 4:00-ish Pacific Time.