It's time to start thinking about your 2009 income taxes.
Will you owe money, will you be owed money?
If you plan and project your tax situation now, you'll be able to accrue / save extra cash and be prepared for the april 15th tax bill.
On the other hand, you would add withholding allowances to keep extra money and eliminate the wait that you would otherwise have for the federal government to pay you back.
Another item to think about is multi-state income - do you work in more than one state? will your employer report such earnings? many state income taxes vary. plan with the right numbers.