We have been seeing a steady decline in traffic all week. Today is the lowest day, but it is to be expected with the holiday next week. Looking at previous years the week before christmas has always experienced this steady decline. After new years we see a big spike back up to normal traffic and a lot of times higher than before xmas/new years. If you are in the USA and don't have a seasonal business (xmas related) I wouldn't worry about it until after New years....unless you see big drops in your actual keywords you know bring in a lot of referrals. Those keyword drops are definitely bad, otherwise traffic declines can be expected around this time.