Millions of Americans endured a slow, slippery return to work Monday as the Eastern Seaboard dug out from a record-setting blizzard that killed at least 41 people. Transit systems and airports were recovering from a weekend of paralysis, but forecasters warned that refreezing of melting snow could make roads slick and dangerous. Non-essential federal workers were ordered to stay home in Washington, D.C., Maryland and Virginia as officials encouraged residents to stay off the roads and allow the blizzard cleanup effort to continue.