Saint Patrick's Day, 2008 is not on March 17th as usual but, rather, on March 15th. This shift is because March 17th falls during the Christian Holy Week. The Roman Catholic Church moves Saint Patrick's Day whenever it coincides with the Holy Week, a coincidence which last occurred in 1940 and will next occur in 2160.
In quickly polling around, it seems as though very few people are aware of the date shift. In fact, even my wall calendar has the date wrong. Don't get me wrong, I like a good drinking holiday as much as the next person but if you're going to hijack a holiday and use it for drinking, you really should do the hijacking correctly.
Drinking on the wrong day makes the as-yet-unressurrected baby Jesus cry. Don't do it!