Riding can definitely be easier after dark: less traffic and some traffic lights on blinking mode. If you have decent lights, visibility problems are lessened.

Crime is another issue. A lot of people feel less safe after dark. It doesn't bother me much, but my family is another story. The last two nights I set out to walk to work (after dark since DST ended a short time ago) and my son and DIL insisted on driving me because they think it's too dangerous to walk in our neighborhood at night.