What exactly is the business milage deduction? You can deduct any unreimbursed business miles at 51 cents a mile. Business miles are miles from your place of work to any other location and back. They do not include commuting to and from your job or if you are self employed, to and from your office. But see this link for an interesting perspective on claiming milage if you have your home office and an office outside the home:
http://www.consultingmentor.com/Article.asp?101
Here is a link to the IRS site for more info:
http://www.irs.gov/newsroom/article/0,,id=232017,00.html
Remember to keep an milage log to document your miles. It is the only proof prepared totally by the taxpayer that the IRS has to accept.