The IRS figures are generous by our perspective, but accurately reflect situations like a sales rep. for a manufacturer, who operates a newish, American four door sedan and really can't be expected to drive clients around in a 'stachian car. In reality, encouraging a potential client to drop a major amount on your company after you take him to lunch in your 15 YO Metro, wouldn't really end well.
The only thing I would add is that, I spent many years operating various light trucks in my construction business, and it was always heavily stressed by my accountants to keep a well documented log of business miles travelled, including destination, client being billed, and starting and ending ODO readings. I'm sure it's tough to resist the urge to use a tech. solution for this, but I always used a small bound journal. My thinking is that an old work journal, that's been in the car a few years, with coffee stains and ten different ink and pencil entries, looks a lot more authentic in an audit, compared to a freshly printed spreadsheet.