While I wouldn't go as far as Simon from The Dossing Times in accusing David McWilliams of coming to "plain silly" conclusions which represent an "abuse of statistics", I do think Simon has a much simpler (and less time and data intensive) method of discovering why the increase looked so big than mine: McWilliams just compared January 2008 with August 2008, and saw a huge increase. But there are seasonal effects here, as Simon correctly points out when you look year to year, which make this increase look more than regular.
So it's more of a slight gaffe than a deliberate abuse of statistics, and McWilliams should know better, but he has shown us (or at least to me) data source when looking back at Irish emigration patterns. A more sophisticated analysis might be in order here. Anyone interested in helping?