I don't think that there are going to be many problems with the PC (or Mac) itself or the operating system. Any problems that arise will most likely appear in added software, particularly anything that uses a date for any reason. So if you have any databases or address books out there that contain a date field then you will need to take a look at them individually.

As Escamillo says, set your machine date forward and see what happens. When performing this test don't do any serious work. Try saving and retrieving files with each piece of added software that you have. Only work with test data that you can safely throw away. Then if things go wrong you won't lose your good stuff.

It might also be wise to back up all of your important data before the end of the year (but you do that regularly anyway, don't you)

Bert.