Even though few clients do it, I’ve always advised that they keep track of their actual vehicle expenses so that we can compare those with what we come up with via the IRS’s standard rate method. Since the IRS standard rate has to apply to pretty much every kind of vehicle regardless of the number of miles driven per year, it can’t possibly be an accurate representation for everyone.
I came across this interesting little chart of per mile vehicle costs in the most recent TaxCoach report, which they assembled from AAA data.
Tax Guru - Ker$tetter Letter 