However, be warned that if you claim more than 9, your employer is required to submit a copy of the W-4 to the IRS with their quarterly payroll tax return.
When I was doing large payrolls, the W-4 had to be sent to IRS within 10 days by the employer.
I looked into this. It seems my info is about 4 years out of date. Effective April 14, 2005, IRS passed a new reg that relieved employers of the responsibility of submitting W-4s to IRS, except when specifically requested. In the announcement, IRS claimed they had enough info elsewhere to detect abuses, without having copies of the W-4s. So, presently, employers should not automatically be sending any W-4s to IRS. Rest easy.