Please see for reference IRS publication 526 - www.irs.gov/pub/irs-pdf/p526.pdf
You cannot deduct the value of your time or services, including
- the value of income lost while you work as an unpaid volunteer for a qualified organization.
So "Can I write-off the hours I donate to the church?" - No you may not.
Although you cannot deduct the value of your services given to a qualified organization, you may be able to deduct some amounts you pay in giving services to a qualified organization.
For instance - you can deduct unreimbursed out-of-pocket expenses, such as the cost of gas and oil, that are directly related to the use of your car in giving services to a charitable organization. You cannot deduct general repair and maintenance expenses, depreciation, registration fees, or the costs of tires or insurance.
If you do not want to deduct your actual expenses, you can use a standard mileage rate of 14 cents a mile (for 2010) to figure your contribution.